do----while Loop
‘C’ program implements a post-test loop using a structure called a do...while loop.
The do...while loop structure, is used to execute a block of statements in a unspecified number of times while a condition is true.
If the condition is false on the first pass, the statements are not executed.
/* Demonstrate while and do...while loops. */
#include<stdio.h>
int main(void)
{
//local declarations
int loopCount;
//statements
loopCount=5;
printf("while loop:");
while(loopCount>0)
print("%3d", loopcount--);
printf("\n\n");
loopCount=5;
printf("do...while loop:");
do
printf("%3d", looCount--);
while(loopCount>0);
printf("\n");
return 0;
} //end main
OUTPUT:
while loop: 5 4 3 2 1
do...while loop: 5 4 3 2 1
Loop comparison in Counter – Controlled Loop
Pre-test loop
|
Post-test loop
| ||
Initialization:
|
1
|
Initialization:
|
1
|
Number of tests:
|
n+1
|
Number of tests:
|
n
|
Action executed:
|
n
|
Action executed:
|
n
|
Updating executed:
|
n
|
Updating executed:
|
n
|
Minimum iterations:
|
0
|
Minimum iterations:
|
1
|
Comparison of while and for loop
Comparison of do...while and while loops
Break Statements in Loops
The break statement, when executed in a while, for, do...while or switch statement, causes immediate exit for that loop.
The common use of the break statement is to skip from the loop.
Eliminating the Break in Loops
Continue Statement
The continue statement, when executed in a while, for or do...while structure, skips the remaining statements in the body of that structure and proceeds with the next iteration of the loops.
Unlike break, the continue statement doesn’t terminate a loop, but transfers control to the testing expression (in while and do...while loops) or the update expression (in for loops).
Summary
At loop is a programming structure that allows an action to repeat until the program meets a given condition.
In pre-test loop each iteration, the program tests the condition first before executing the loops block.
In post-test loop each iteration, the program executes the loops block first and tests against a condition.
A while loop is an event controlled loop. It is a control flow statement that, allows the code to be executed repeatedly based on a given condition.
A ‘for loop’ is a pre-test loop that includes three expressions in its header:
-Loop initialization statement
-Limit test expression
-Loop update statement
The do...while loop structure, is used to execute a block of statements in a unspecified number of times while a condition is true. If the condition is false on the first pass, the statements are not executed.
