Programming iOS 6, 3rd Edition

Flow Control and Conditions

Basic flow control is fairly simple and usually involves a condition in parentheses and a block of conditionally executed code in curly braces. These curly braces constitute a new scope, into which new variables can be introduced. So, for example:

if (x == 7) {
    int i = 0;
    i += 1;
}

After the closing curly brace in the fourth line, the i introduced in the second line has ceased to exist, because its scope is the inside of the curly braces. If the contents of the curly braces consist of a single statement, the curly braces can be omitted, but I would advise beginners against this shorthand, as you can confuse yourself. A common beginner mistake (which will be caught by the compiler) is forgetting the parentheses around the condition. The full set of flow control statements is given in K&R Chapter 3, and I’ll just summarize them schematically here (Example 1-1).

Example 1-1. The C flow control constructs

if (condition) {
    statements;
}

if (condition) {
    statements;
} else {
    statements;
}

if (condition) {
    statements;
} else if (condition) {
    statements;
} else {
    statements;
}

while (condition) {
    statements;
}

do {
    statements;
} while (condition);

for (before-all; condition; after-each) {
    statements;
}

The if...else if...else structure can have as many else if blocks as needed, and the else block is optional. Instead of an extended if...else if...else if...else structure, when the conditions would consist of comparing various values against a single value, you can ...