The while statement takes the form:

        while( <condition> ) <statement>

where:

while is a keyword.followed by a paranthesized condition

The condition is an expression which evaluates to either true or false.

and the body of the loop is a single statement.

Semantics

While the condition is true, execute the statement.

in other words:

1. Evaluate the condition,
2. If it is true, execute the statement and then repeat from step 1.
3. If it is false, the while statement is done.

Note: we can use compound statements to execute multiple statements when the while condition is true. See compound statements below. For example,

while( <condition> )

{

<statement>

<statement>

<statement>

<statement>

}

Compound Statements

The compound statement groups an arbitrary number of other statments into a single statement. It is sometimes also called a block. It takes the form:

        {

             <statement>

             <statement>

             ...

             <statement>

        }

Semantics

When a compound statement is executed, each of the statements in the block are executed sequentially.

How do we translate this looping construct to C?

We use a while statement

Essential elements of a loop:

There are four essential elements to every loop:

Condition initialization

the condition determining if the loop iterates must be initialized before the first test.

Condition test

the condition is tested to see if the body of the loop is to be executed.

Loop body

the steps to be executed, which MUST include

Condition update

a statement which modifies the condition such that at some time it will become false.

For example:

        i = 0;                /* loop initialization  */

        while( i < 100 )      /* loop test            */

             i = i + 1;       /* loop body and update */

For the stock program, the loop condition is:

        ...

        while there are more stocks to proccess

             ...

How do we tell if there are more stocks?

We will look at three ways: Counting, special data values, and End of File