Repetition Structures in C Programming: While, Do-While, and For Loops, Slides of Computer Engineering and Programming

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Repetition Structures

Lecture 10

Repetition Structures

• Repetition structures are used to repeat

statements or blocks of code.

• The decision whether to repeat the code is based

on the evaluation of a logical expression. If the

expression is true, the code is executed. If false,

the code is not executed.

• Repetition structures may repeat the code a

definite number of times (usually for loops) or an

indefinite number of times (usually while or do

while loops).

While Loops (Syntax)

The syntax of a while loop is:

while ( logical expression is true ) statement ;

or

while ( logical expression is true )

statement ;

statement ;

While Loops

/* This program associates letter grades with

numeric test scores. It continues to request

input until the user types in a 0 and then it

terminates with a message. */

#include <stdio.h>

int main ( )

int score ;

While Loops

else if (score >= 60)

printf ("Your score of %d is a D\n", score) ;

else if (score != 0)

printf ("Your score of %d is an E\n", score) ;

else

printf ("Terminating at your request.\n\n") ;

} /* End of While loop */

} /* End of "main" function */

Do-While Loops (Syntax)

do statement ; while ( logical expr is true ) ;

or, more commonly do { statement ; statement ; } while ( logical expression is true ) ;

Do-While Loops

do { printf ("enter a test score (0 to quit) >") ; scanf ("%d", &score) ; if (score >= 90) printf ("Your score of %d is a A\n", score) ; else if (score >= 80 && score <90) printf ("Your score of %d is a B\n", score) ; else if (score >= 70) printf ("Your score of %d is a C\n", score) ;

Do-While Loops

else if (score >= 60)

printf ("Your score of %d is a D\n", score) ;

else if (score != 0)

printf ("Your score of %d is an E\n", score) ;

else

printf ("Terminating at your request.\n\n") ;

} while (score != 0) ;

For Loops

for ( expr1 ; expr2 ; expr3 ) { statement(s) ; }

Expression2 is the logical expression to be

evaluated as true or false. It does NOT need to

contain any of the variables that are in

expression1. It gets evaluated after expression

and again after expression3.

For Loops

for ( expr1 ; expr2 ; expr3 ) { statement(s) ; }

Expression3 defines changes to conditions. It

can be multiple expressions separated by

commas. It gets executed after the statements

in the loop are executed. The expressions do

NOT have to be related to either those in

expression1 or in expression2 (but they often

are). Docsity.com

Simple For Loop Example

int counter;

for (counter = 1; counter <= 10; counter++)

printf ("The counter value is: %2d\n",

counter);

Equivalency of While Loop vs. For

Loop

The Loop: expression1 ; while ( expression2 ) { statement ; expression3 ; }

Is Equivalent to:

for ( expr1 ; expr2 ; expr3 ) statement ;

Simple While Loop Example

int counter ;

counter = 1 ; while ( counter <= 10 ) { printf ("The counter value is: %2d\n", counter) ; counter++ ; }

Example of For Loop

#include <stdio.h>

int main ( )

int k, n ;

for (k = 1, n = 12 ; k < 9 && n > 6 ; k++, n--)

printf ("k=%d, n=%d\n" , k , n ) ;