Head First C

Chapter 1. Getting Started with C: Diving in

Want to get inside the computer’s head?

Need to write high-performance code for a new game? Program an Arduino? Or use that advanced third-party library in your iPhone app? If so, then C’s here to help. C works at a much lower level than most other languages, so understanding C gives you a much better idea of what’s really going on. C can even help you better understand other languages as well. So dive in and grab your compiler, and you’ll soon get started in no time.

C is a language for small, fast programs

The C language is designed to create small, fast programs. It’s lower-level than most other languages; that means it creates code that’s a lot closer to what machines really understand.

The way C works

Computers really only understand one language: machine code, a binary stream of 1s and 0s. You convert your C code into machine code with the aid of a compiler.

C is used where speed, space, and portability are important. Most operating systems are written in C. Most other computer languages are also written in C. And most game software is written in C.

Note

There are three C standards that you may stumble across. ANSI C is from the late 1980s and is used for the oldest code. A lot of things were fixed up in the C99 standard from 1999. And some cool new language features were added in the current standard, C11, released in 2011. The differences between the different versions aren’t huge, and we’ll point them out along the way.

Sharpen your pencil

Try to guess what each of these code fragments does.

Sharpen your pencil: Solution

Don’t worry if you don’t understand all of this yet. Everything is explained in greater detail later in the book.

But what does a complete C program look like?

To create a full program, you need to enter your code into a C source file. C source files can be created by any text editor, and their filenames usually end with .c.

Note

This is just a convention, but you should follow it.

Let’s have a look at a typical C source file.

So let’s look at the main() function in a little more detail.

The main() Function Up Close

The computer will start running your program from the main() function. The name is important: if you don’t have a function called main(), your program won’t be able to start.

The main() function has a return type of int. So what does this mean? Well, when the computer runs your program, it will need to have some way of deciding if the program ran successfully or not. It does this by checking the return value of the main() function. If you tell your main() function to return 0, this means that the program was successful. If you tell it to return any other value, this means that there was a problem.

The function name comes after the return type. That’s followed by the function parameters if there are any. Finally, we have the function body. The function body must be surrounded by braces.

Geek Bits

The printf() function is used to display formatted output. It replaces format characters with the values of variables, like this:

You can include as many parameters as you like when you call the printf() function, but make sure you have a matching % format character for each one.

Note

If you want to check the exit status of a program, type:

echo %ErrorLevel%

in Windows, or:

echo $?

in Linux or on the Mac.

Code Magnets

The College Blackjack Team was working on some code on the dorm fridge, but someone mixed up the magnets! Can you reassemble the code from the magnets?

Code Magnets Solution

The College Blackjack Team was working on some code on the dorm fridge, but someone mixed up the magnets! You were to reassemble the code from the magnets.

There are no Dumb Questions

Q:	What does card_name[0] mean?
A:	It’s the first character that the user typed. So if he types 10, card_name[0] would be 1.
Q:	Do you always write comments using /* and */?
A:	If your compiler supports the C99 standard, then you can begin a comment with //. The compiler treats the rest of that line as a comment.
Q:	How do I know which standard my compiler supports?
A:	Check the documentation for your compiler. gcc supports all three standards: ANSI C, C99, and C11.

But how do you run the program?

C is a compiled language. That means the computer will not interpret the code directly. Instead, you will need to convert—or compile—the human-readable source code into machine-readable machine code.

To compile the code, you need a program called a compiler. One of the most popular C compilers is the GNU Compiler Collection or gcc. gcc is available on a lot of operating systems, and it can compile lots of languages other than C. Best of all, it’s completely free.

Here’s how you can compile and run the program using gcc.

Geek Bits

You can compile and run your code on most machines using this trick:

This command will run the new program only if it compiles successfully. If there’s a problem with the compile, it will skip running the program and simply display the errors on the screen.

Do this!

You should create the cards.c file and compile it now. We’ll be working on it more and more as the chapter progresses.

Test Drive

Let’s see if the program compiles and runs. Open up a command prompt or terminal on your machine and try it out.

The program works!

Congratulations! You have compiled and run a C program. The gcc compiler took the human-readable source code from cards.c and converted it into computer-readable machine code in the cards program. If you are using a Mac or Linux machine, the compiler will have created the machine code in a file called cards. But on Windows, all programs need to have a .exe extension, so the file will be called cards.exe.

There are no Dumb Questions

Q:	Why do I have to prefix the program with ./ when I run it on Linux and the Mac?
A:	On Unix-style operating systems, programs are run only if you specify the directory where they live or if their directory is listed in the PATH environment variable.

The C language doesn’t support strings out of the box.

Note

But there are a number of C extension libraries that do give you strings.

C is more low-level than most other languages, so instead of strings, it normally uses something similar: an array of single characters. If you’ve programmed in other languages, you’ve probably met an array before. An array is just a list of things given a single name. So card_name is just a variable name you use to refer to the list of characters entered at the command prompt. You defined card_name to be a two-character array, so you can refer to the first and second character as char_name[0] and char_name[1]. To see how this works, let’s take a deeper dive into the computer’s memory and see how C handles text...

Strings Way Up Close

Strings are just character arrays. When C sees a string like this:

s = "Shatner"

it reads it like it was just an array of separate characters:

Each of the characters in the string is just an element in an array, which is why you can refer to the individual characters in the string by using an index, like s[0] and s[1].

Don’t fall off the end of the string

But what happens when C wants to read the contents of the string? Say it wants to print it out. Now, in a lot of languages, the computer keeps pretty close track of the size of an array, but C is more low-level than most languages and can’t always work out exactly how long an array is. If C is going to display a string on the screen, it needs to know when it gets to the end of the character array. And it does this by adding a sentinel character.

The sentinel character is an additional character at the end of the string that has the value \0. Whenever the computer needs to read the contents of the string, it goes through the elements of the character array one at a time, until it reaches \0. That means that when the computer sees this:

s = "Shatner"

it actually stores it in memory like this:

That’s why in our code we had to define the card_name variable like this:

char card_name[3];

The card_name string is only ever going to record one or two characters, but because strings end in a sentinel character we have to allow for an extra character in the array.

There are no Dumb Questions

Q:	Why are the characters numbered from 0? Why not 1?
A:	The index is an offset: it’s a measure of how far the character is from the first character.
Q:	Why?
A:	The computer will store the characters in consecutive bytes of memory. It can use the index to calculate the location of the character. If it knows that c[0] is at memory location 1,000,000, then it can quickly calculate that c[96] is at 1,000,000 + 96.
Q:	Why does it need a sentinel character? Doesn’t it know how long the string is?
A:	Usually, it doesn’t. C is not very good at keeping track of how long arrays are, and a string is just an array.
Q:	It doesn’t know how long arrays are???
A:	No. Sometimes the compiler can work out the length of an array by analyzing the code, but usually C relies on you to keep track of your arrays.
Q:	Does it matter if I use single quotes or double quotes?
A:	Yes. Single quotes are used for individual characters, but double quotes are always used for strings.
Q:	So should I define my strings using quotes (″) or as explicit arrays of characters?
A:	Usually you will define strings using quotes. They are called string literals, and they are easier to type.
Q:	Are there any differences between string literals and character arrays?
A:	Only one: string literals are constant.
Q:	What does that mean?
A:	It means that you can’t change the individual characters once they are created.
Q:	What will happen if I try?
A:	It depends on the compiler, but gcc will usually display a bus error.
Q:	A bus error? What the heck’s a bus error?
A:	C will store string literals in memory in a different way. A bus error just means that your program can’t update that piece of memory.

Painless Operations

Not all equals signs are equal.

In C, the equals sign ( =) is used for assignment. But a double equals sign ( ==) is used for testing equality.

If you want to increase or decrease a variable, then you can save space with the += and -= assignments.

Finally, if you want to increase or decrease a variable by 1, use ++ and --.

Two types of command

So far, every command you’ve seen has fallen into one of the following two categories.

Do something

Most of the commands in C are statements. Simple statements are actions; they do things and they tell us things. You’ve met statements that define variables, read input from the keyboard, or display data to the screen.

Sometimes you group statements together to create block statements. Block statements are groups of commands surrounded by braces.

Do something only if something is true

Control statements such as if check a condition before running the code:

if statements typically need to do more than one thing when a condition is true, so they are often used with block statements:

Do you need braces?

Block statements allow you to treat a whole set of statements as if they were a single statement. In C, the if condition works like this:

if (countdown == 0)
  
do_this_thing();

The if condition runs a single statement. So what if you want to run several statements in an if? If you wrap a list of statements in braces, C will treat them as though they were just one statement:

if (x == 2) {
  
call_whitehouse();
  
sell_oil();
  
x = 0;

}

C coders like to keep their code short and snappy, so most will omit braces on if conditions and while loops. So instead of writing:

if (x == 2) {
    
puts("Do something");

}

most C programmers write:

if (x == 2)
    
puts("Do something");

Here’s the code so far

/* * Program to evaluate face values. * Released under the Vegas Public License. * (c)2014 The College Blackjack Team. */ #include <stdio.h> #include <stdlib.h> int main() { char card_name[3]; puts("Enter the card_name: "); scanf("%2s", card_name); int val = 0; if (card_name[0] == 'K') { val = 10; } else if (card_name[0] == 'Q') { val = 10; } else if (card_name[0] == 'J') { val = 10; } else if (card_name[0] == 'A') { val = 11; } else { val = atoi(card_name); } printf("The card value is: %i\n", val); return 0; }

Card counting? In C?

Card counting is a way to increase your chances of winning at blackjack. By keeping a running count as the cards are dealt, a player can work out the best time to place large bets and the best time to place small bets. Even though it’s a powerful technique, it’s really quite simple.

How difficult would this be to write in C? You’ve looked at how to make a single test, but the card-counting algorithm needs to check multiple conditions: you need to check that a number is >= 3 as well as checking that it’s <= 6.

You need a set of operations that will allow you to combine conditions together.

There’s more to booleans than equals...

So far, you’ve looked at if statements that check if a single condition is true, but what if you want to check several conditions? Or check if a single condition is not true?

&& checks if two conditions are true

The and operator ( &&) evaluates to true, only if both conditions given to it are true.

The and operator is efficient: if the first condition is false, then the computer won’t bother evaluating the second condition. It knows that if the first condition is false, then the whole condition must be false.

II checks if one of two conditions is true

The or operator ( ||) evaluates to true, if either condition given to it is true.

If the first condition is true, the computer won’t bother evaluating the second condition. It knows that if the first condition is true, the whole condition must be true.

! flips the value of a condition

! is the not operator. It reverses the value of a condition.

Geek Bits

In C, boolean values are represented by numbers. To C, the number 0 is the value for false. But what’s the value for true? Anything that is not equal to 0 is treated as true. So there is nothing wrong in writing C code like this:

int people_moshing = 34;
if (people_moshing)
    take_off_glasses();

In fact, C programs often use this as a shorthand way of checking if something is not 0.

Exercise

You are going to modify the program so that it can be used for card counting. It will need to display one message if the value of the card is from 3 to 6. It will need to display a different message if the card is a 10, Jack, Queen, or King.

int main()
{
    char card_name[3];
    puts("Enter the card_name: ");
    scanf("%2s", card_name);
    int val = 0;
    if (card_name[0] == 'K') {
        val = 10;
    } else if (card_name[0] == 'Q') {
        val = 10;
    } else if (card_name[0] == 'J') {
        val = 10;
    } else if (card_name[0] == 'A') {
        val = 11;
    } else {
        val = atoi(card_name);
    }
    /* Check if the value is 3 to 6 */
    if _______________________________
        puts("Count has gone up");
    /* Otherwise check if the card was 10, J, Q, or K */
    else if ______________________________
        puts("Count has gone down");
    return 0;
}

The Polite Guide to Standards

The ANSI C standard has no value for true and false. C programs treat the value 0 as false, and any other value as true. The C99 standard does allow you to use the words true and false in your programs—but the compiler treats them as the values 1 and 0 anyway.

Exercise Solution

You were to modify the program so that it can be used for card counting. It needed to display one message if the value of the card is from 3 to 6. It needed to display a different message if the card is a 10, Jack, Queen, or King.

There are no Dumb Questions

Q:	Why not just | and &?
A:	You can use & and | if you want. The & and | operators will always evaluate both conditions, but && and || can often skip the second condition.
Q:	So why do the & and | operators exist?
A:	Because they do more than simply evaluate logical conditions. They perform bitwise operations on the individual bits of a number.
Q:	Huh? What do you mean?
A:	Well, 6 & 4 is equal to 4, because if you checked which binary digits are common to 6 (110 in binary) and 4 (100 in binary, you get 4 (100).

Test Drive

Let’s see what happens when you compile and run the program now:

The code works. By combining multiple conditions with a boolean operator, you check for a range of values rather than a single value. You now have the basic structure in place for a card counter.

The Compiler Exposed

This week’s interview: What Has gcc Ever Done for Us?

• Head First: May I begin by thanking you, gcc, for finding time in your very busy schedule to speak to us.

• gcc: That’s not a problem, my friend. A pleasure to help.

• Head First: gcc, you can speak many languages, is that true?

• gcc: I am fluent in over six million forms of communication...

• Head First: Really?

• gcc: Just teasing. But I do speak many languages. C, obviously, but also C++ and Objective-C. I can get by in Pascal, Fortran, PL/I, and so forth. Oh, and I have a smattering of Go...

• Head First: And on the hardware side, you can produce machine code for many, many platforms?

• gcc: Virtually any processor. Generally, when a hardware engineer creates a new type of processor, one of the first things she wants to do is get some form of me running on it.

• Head First: How have you achieved such incredible flexibility?

• gcc: My secret, I suppose, is that there are two sides to my personality. I have a frontend, a part of me that understands some type of source code.

• Head First: Written in a language such as C?

• gcc: Exactly. My frontend can convert that language into an intermediate code. All of my language frontends produce the same sort of code.

• Head First: You say there are two sides to your personality?

• gcc: I also have a backend: a system for converting that intermediate code into machine code that is understandable on many platforms. Add to that my knowledge of the particular executable file formats for just about every operating system you’ve ever heard of...

• Head First: And yet, you are often described as a mere translator. Do you think that’s fair? Surely that’s not all you are.

• gcc: Well, of course I do a little more than simple translation. For example, I can often spot errors in code.

• Head First: Such as?

• gcc: Well, I can check obvious things such as misspelled variable names. But I also look for subtler things, such as the redefinition of variables. Or I can warn the programmer if he chooses to name variables after existing functions and so on.

• Head First: So you check code quality as well, then?

• gcc: Oh, yes. And not just quality, but also performance. If I discover a section of code inside a loop that could work equally well outside a loop, I can very quietly move it.

• Head First: You do rather a lot!

• gcc: I like to think I do. But in a quiet way.

• Head First: gcc, thank you.

BE the Compiler

Each of the C files on this page represents a complete source file. Your job is to play compiler and determine whether each of these files will compile, and if not, why not. For extra bonus points, say what you think the output of each compiled file will be when run, and whether you think the code is working as intended.

A

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1)
        card = card - 1;
        if (card < 7)
            puts("Small card");
    else {
      puts("Ace!");
    }
    return 0;
}

B

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1) {
        card = card - 1;
        if (card < 7)
            puts("Small card");
    else
      puts("Ace!");
    }
    return 0;
}

C

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1) {
        card = card - 1;
        if (card < 7)
            puts("Small card");
    } else
      puts("Ace!");
    return 0;
}

D

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1) {
        card = card - 1;
        if (card < 7)
            puts("Small card");
    else
      puts("Ace!");
    return 0;
}

BE the Compiler Solution

Each of the C files on this page represents a complete source file. Your job is to play compiler and determine whether each of these files will compile, and if not, why not. For extra bonus points, say what you think the output of each compiled file will be when run, and whether you think the code is working as intended.

A

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1)
        card = card - 1;
        if (card < 7)
            puts("Small card");
    else {
      puts("Ace!");
    }
    return 0;
}

The code compiles. The program displays “Small card.” But it doesn’t work properly because the else is attached to the wrong if.

B

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1) {
        card = card - 1;
        if (card < 7)
            puts("Small card");
    else
      puts("Ace!");
    }
    return 0;
}

The code compiles. The program displays nothing and is not really working properly because the else is matched to the wrong if.

C

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1) {
        card = card - 1;
        if (card < 7)
            puts("Small card");
    } else
      puts("Ace!");
    return 0;
}

The code compiles. The program displays “Ace!” and is properly written.

D

#include <stdio.h>

int main()
{
    int card = 1;
    if (card > 1) {
        card = card - 1;
        if (card < 7)
            puts("Small card");
    else
      puts("Ace!");
    return 0;
}

The code won’t compile because the braces are not matched.

What’s the code like now?

int main() { char card_name[3]; puts("Enter the card_name: "); scanf("%2s", card_name); int val = 0; if (card_name[0] == 'K') { val = 10; } else if (card_name[0] == 'Q') { val = 10; } else if (card_name[0] == 'J') { val = 10; } else if (card_name[0] == 'A') { val = 11; } else { val = atoi(card_name); } /* Check if the value is 3 to 6 */ if ((val > 2) && (val < 7)) puts("Count has gone up"); /* Otherwise check if the card was 10, J, Q, or K */ else if (val == 10) puts("Count has gone down"); return 0; }

C programs often need to check the same value several times and then perform very similar pieces of code for each case.

Now, you can just use a sequence of if statements, and that will probably be just fine. But C gives you an alternative way of writing this kind of logic.

C can perform logical tests with the switch statement.

Pulling the ol’ switcheroo

Sometimes when you’re writing conditional logic, you need to check the value of the same variable over and over again. To prevent you from having to write lots and lots of if statements, the C language gives you another option: the switch statement.

The switch statement is kind of like an if statement, except it can test for multiple values of a single variable:

When the computer hits a switch statement, it checks the value it was given, and then looks for a matching case. When it finds one, it runs all of the code that follows it until it reaches a break statement. The computer keeps going until it is told to break out of the switch statement.

Watch it!

Missing breaks can make your code buggy.

Most C programs have a break at the end of each case section to make the code easier to understand, even at the cost of some efficiency.

Sharpen your pencil

Let’s look at that section of your cards program again:

int val = 0;
if (card_name[0] == 'K') {
    val = 10;
} else if (card_name[0] == 'Q') {
    val = 10;
} else if (card_name[0] == 'J') {
    val = 10;
} else if (card_name[0] == 'A') {
    val = 11;
} else {
    val = atoi(card_name);
}

Do you think you can rewrite this code using a switch statement? Write your answer below:

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

______________________________

Sharpen your pencil: Solution

You were to rewrite the code using a switch statement.

Bullet Points

• switch statements can replace a sequence of if statements.

• switch statements check a single value.

• The computer will start to run the code at the first matching case statement.

• It will continue to run until it reaches a break or gets to the end of the switch statement.

• Check that you’ve included breaks in the right places; otherwise, your switches will be buggy.

There are no Dumb Questions

Q:	Why would I use a switch statement instead of an if?
A:	If you are performing multiple checks on the same variable, you might want to use a switch statement.
Q:	What are the advantages of using a switch statement?
A:	There are several. First: clarity. It is clear that an entire block of code is processing a single variable. That’s not so obvious if you just have a sequence of if statements. Secondly, you can use fall-through logic to reuse sections of code for different cases.
Q:	Does the switch statement have to check a variable? Can’t it check a value?
A:	Yes, it can. The switch statement will simply check that two values are equal.
Q:	Can I check strings in a switch statement?
A:	No, you can’t use a switch statement to check a string of characters or any kind of array. The switch statement will only check a single value.

Sometimes once is not enough...

You’ve learned a lot about the C language, but there are still some important things to learn. You’ve seen how to write programs for many different situations, but there is one fundamental thing that we haven’t really looked at yet. What if you want your program to do something again and again and again?

Using while loops in C

Loops are a special type of control statement. A control statement decides if a section of code will be run, but a loop statement decides how many times a piece of code will be run.

The most basic kind of loop in C is the while loop. A while loop runs code over and over and over as long as some condition remains true.

Do you do while?

There’s another form of the while loop that checks the loop condition after the loop body is run. That means the loop always executes at least once. It’s called the do...while loop:

do {
  
/* Buy lottery ticket */

} while(have_not_won);

Loops often follow the same structure...

You can use the while loop anytime you need to repeat a piece of code, but a lot of the time your loops will have the same kind of structure:

• Do something simple before the loop, like set a counter.

• Have a simple test condition on the loop.

• Do something at the end of a loop, like update a counter.

For example, this is a while loop that counts from 1 to 10:

Loops like this have code that prepares variables for the loop, some sort of condition that is checked each time the loop runs, and finally some sort of code at the end of the loop that updates a counter or something similar.

...and the for loop makes this easy

Because this pattern is so common, the designers of C created the for loop to make it a little more concise. Here is that same piece of code written with a for loop:

for loops are actually used a lot in C—as much, if not more than, while loops. Not only do they make the code slightly shorter, but they’re also easier for other C programmers to read, because all of the code that controls the loop—the stuff that controls the value of the counter variable—is now contained in the for statement and is taken out of the loop body.

Every for loop needs to have something in the body.

You use break to break out...

You can create loops that check a condition at the beginning or end of the loop body. But what if you want to escape from the loop from somewhere in the middle? You could always restructure your code, but sometimes it’s just simpler skip out of the loop immediately using the break statement:

A break statement will break you straight out of the current loop, skipping whatever follows it in the loop body. breaks can be useful because they’re sometimes the simplest and best way to end a loop. But you might want to avoid using too many, because they can also make the code a little harder to read.

Watch it!

The break statement is used to break out of loops and also switch statements.

Make sure that you know what you’re break ing out of when you break.

...and continue to continue

If you want to skip the rest of the loop body and go back to the start of the loop, then the continue statement is your friend:

Tales from the Crypt

breaks don’t break if statements.

On January 15, 1990, AT&T’s long-distance telephone system crashed, and 60,000 people lost their phone service. The cause? A developer working on the C code used in the exchanges tried to use a break to break out of an if statement. But break s don’t break out of if s. Instead, the program skipped an entire section of code and introduced a bug that interrupted 70 million phone calls over nine hours.

Writing Functions Up Close

Before you try out your new loop mojo, let’s go on a detour and take a quick look at functions.

So far, you’ve had to create one function in every program you’ve written, the main() function:

Pretty much all functions in C follow the same format. For example, this is a program with a custom function that gets called by main():

The larger() function is slightly different from main() because it takes arguments or parameters. An argument is just a local variable that gets its value from the code that calls the function. The larger() function takes two arguments— a and b—and then it returns the value of whichever one is larger.

The Polite Guide to Standards

The main() function has an int return type, so you should include a return statement when you get to the end. But if you leave the return statement out, the code will still compile—though you may get a warning from the compiler. A C99 compiler will insert a return statement for you if you forget. Use -std=c99 to compile to the C99 standard.

Void Functions Up Close

Most functions in C have a return value, but sometimes you might want to create a function that has nothing useful to return. It might just do stuff rather than calculate stuff. Normally, functions always have to contain a return statement, but not if you give your function the return type void:

In C, the keyword void means it doesn’t matter. As soon as you tell the C compiler that you don’t care about returning a value from the function, you don’t need to have a return statement in your function.

There are no Dumb Questions

Q:	If I create a void function, does that mean it can’t contain a return statement?
A:	You can still include a return statement, but the compiler will most likely generate a warning. Also, there’s no point to including a return statement in a void function.
Q:	Really? Why not?
A:	Because if you try to read the value of your void function, the compiler will refuse to compile your code.

Chaining Assignments

Almost everything in C has a return value, and not just function calls. In fact, even things like assignments have return values. For example, if you look at this statement:

x = 4;

It assigns the number 4 to a variable. The interesting thing is that the expression “ x = 4” itself has the value that was assigned: 4. So why does that matter? Because it means you can do cool tricks, like chaining assignments together:

That line of code will set both x and y to the value 4. In fact, you can shorten the code slightly by removing the parentheses:

y = x = 4;

You’ll often see chained assignments in code that needs to set several variables to the same value.

Mixed Messages

A short C program is listed below. One block of the program is missing. Your challenge is to match the candidate block of code (on the left) with the output that you’d see if the block were inserted. Not all of the lines of output will be used, and some of the lines of output might be used more than once. Draw lines connecting the candidate blocks of code with their matching command-line output.

Exercise

Now that you know how to create while loops, modify the program to keep a running count of the card game. Display the count after each card and end the program if the player types X. Display an error message if the player types a bad card value like 11 or 24.

Mixed Messages Solution

A short C program is listed below. One block of the program is missing. Your challenge was to match the candidate block of code (on the left) with the output that you’d see if the block were inserted. Not all of the lines of output were used. You were to draw lines connecting the candidate blocks of code with their matching command-line output.

Exercise Solution

Now that you know how to create while loops, you were to modify the program to keep a running count of the card game. Display the count after each card and end the program if the player types X. Display an error message if the player types a bad card value like 11 or 24.

Test Drive

Now that the card-counting program is finished, it’s time to take it for a spin. What do you think? Will it work?

The card counting program works!

You’ve completed your first C program. By using the power of C statements, loops, and conditions, you’ve created a fully functioning card counter.

Great job!

Note

Disclaimer: Using a computer for card counting is illegal in many states, and those casino guys can get kinda gnarly. So don’t do it, OK?

There are no Dumb Questions

Q:	Why do I need to compile C? Other languages like JavaScript aren’t compiled, are they?
A:	C is compiled to make the code fast. Even though there are languages that aren’t compiled, some of those—like JavaScript and Python—often use some sort of hidden compilation to improve their speed.
Q:	Is C++ just another version of C?
A:	No. C++ was originally designed as an extension of C, but now it’s a little more than that. C++ and Objective-C were both created to use object orientation with C.
Q:	What’s object orientation? Will we learn it in this book?
A:	Object orientation is a technique to deal with complexity. We won’t specifically look at it in this book.
Q:	C looks a lot like JavaScript, Java, C#, etc.
A:	C has a very compact syntax and it’s influenced many other languages.
Q:	What does gcc stand for?
A:	The Gnu Compiler Collection.
Q:	Why “collection”? Is there more than one?
A:	The Gnu Compiler Collection can be used to compile many languages, though C is probably still the language with which it’s used most frequently.
Q:	Can I create a loop that runs forever?
A:	Yes. If the condition on a loop is the value 1, then the loop will run forever.
Q:	Is it a good idea to create a loop that runs forever?
A:	Sometimes. An infinite loop (a loop that runs forever) is often used in programs like network servers that perform one thing repeatedly until they are stopped. But most coders design loops so that they will stop sometime.

Bullet Points

• A while loop runs code as long as its condition is true.

• A do-while loop is similar, but runs the code at least once.

• The for loop is a more compact way of writing certain kinds of loops.

• You can exit a loop at any time with break.

• You can skip to the loop condition at any time with continue.

• The return statement returns a value from a function.

• void functions don’t need return statements.

• Most expressions in C have values.

• Assignments have values so you can chain them together ( x = y = 0).

Your C Toolbox

You’ve got Chapter 1 under your belt, and now you’ve added C basics to your toolbox. For a complete list of tooltips in the book, see Appendix B.