Sams Teach Yourself C in 21 Days

Basic Program Control 133

6

ThewhileStatement ....................................................................................

Thewhilestatement, also called the whileloop,executes a block of statements as long

as a specified condition is true. The whilestatement has the following form:

while (condition)

statement

conditionis any C expression, and statementis a single or compound C statement.

When program execution reaches a whilestatement, the following events occur:

1. The expression conditionis evaluated.


2. If conditionevaluates to false (that is, zero), the whilestatement terminates, and
   execution passes to the first statement following statement.


3. If conditionevaluates to true (that is, nonzero), the C statement(s) in statement
   are executed.


4. Execution returns to step 1.
   The operation of a whilestatement is shown in Figure 6.3.

FIGURE6.3

The operation of a

whilestatement.

Start

Evaluate

condition

Done

Execute

statements

while (condition)

statements;

FALSE

TRUE

Listing 6.3 is a simple program that uses a whilestatement to print the numbers 1

through 20. (This is the same task that is performed by a forstatement in Listing 6.1.)

LISTING6.3 whilest.c. A simple whilestatement

1: /* Demonstrates a simple while statement */

2:

3: #include <stdio.h>

4:

5: int count;

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