Programming iOS 6, 3rd Edition

Functions

C is a function-based language (K&R 4.1). A function is a block of code defining what should happen; when other code calls (invokes) that function, the function’s code does happen. A function returns a value, which is substituted for the call to that function.

Here’s a definition of a function that accepts an integer and returns its square:

int square(int i) {
    return i * i;
}

Now I’ll call that function:

int i = square(3);

Because of the way square is defined, that is exactly like saying:

int i = 9;

That example is extremely simple, but it illustrates many key aspects of functions.

Let’s analyze how a function is defined:

int square(int i) {
    return i * i;
}

We start with the type of value that the function returns; here, it returns an int.

Then we have the name of the function, which is square.

Then we have parentheses, and here we place the data type and name of any values that this ...