do while Repetition Statement

The do…while repetition statement is similar to the while statement. In the while statement, the loop-continuation condition is tested at the beginning of the loop before the body of the loop is performed. The do…while statement tests the loop-continuation condition after the loop body is performed. Therefore, the loop body will be executed at least

once. When a do…while terminates, execution continues with the statement after the while clause. It’s not necessary to use braces in the do…while statement if there is only one statement in the body. However, the braces are usually included to avoid confusion between the while and do…while statements. For example,

while ( condition )

is normally regarded as the header to a while statement. A do…while with no braces around the single-statement body appears as

do

statement

while ( condition );

which can be confusing. The last line while( condition ); may be misinterpreted by as a while statement containing an empty statement. Thus, to avoid confusion, the do…while with one statement is often written as follows:

do {

statement

} while ( condition );

To eliminate the potential for ambiguity, some programmers always include braces in a do…while statement, even if the braces are not necessary. Infinite loops are caused when the loop-continuation condition in a while, for or do…while statement never becomes false. To prevent this, make sure there is not a semicolon immediately after the header of a while or for the statement. In a counter-controlled loop, make sure the control variable is incremented (or decremented) in the loop. In a sentinel- controlled loop, make sure the sentinel value is eventually input.

The example uses a do…while statement to print the numbers from 1 to 10. The control variable counter is pre-incremented in the loop-continuation test. Note also the use of the braces to enclose the single-statement body of the do…while.

/*using the do/while repetition statement */
#include <stdio.h>

int main( void )
{
int counter = 1;
do{
printf(“%d”, counter);
} while(++ counter<=10 );

return 0;
}

Output

1 2 3 4 5 6 7 8 9 10

Figure

The figure shows the do…while statement flowchart, which makes it clear that the loop-continuation condition does not execute until after the action is performed at least once.