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The while Statement

Executes statement repeatedly until expression evaluates to zero.

while ( expression ) 
   statement

The test of expression takes place before each execution of the loop; therefore, a while loop executes zero or more times. expression must be of an integral type, a pointer type, or a class type with an unambiguous conversion to an integral or pointer type.

A while loop can also terminate when a break, goto, or return within the statement body is executed. Use continue to terminate the current iteration without exiting the while loop. continue passes control to the next iteration of the while loop.

The following code uses a while loop to trim trailing underscores from a string:

// while_statement.cpp

#include <string.h>
#include <stdio.h>
char *trim( char *szSource )
{
    char *pszEOS = 0;

    //  Set pointer to character before terminating NULL
    pszEOS = szSource + strlen( szSource ) - 1;

    //  iterate backwards until non '_' is found 
    while( (pszEOS >= szSource) && (*pszEOS == '_') )
        *pszEOS-- = '\0';

    return szSource;
}
int main()
{
    char szbuf[] = "12345_____";

    printf_s("\nBefore trim: %s", szbuf);
    printf_s("\nAfter trim: %s\n", trim(szbuf));
}

The termination condition is evaluated at the top of the loop. If there are no trailing underscores, the loop never executes.

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