BRANCHING AND LOOPING
ITERATION, FOR LOOPS
The basic format of the for statement is,
for(start condition; continue condition; re-evaulation )
program statement;
Example:
/*sample program using a for statement */
#include <stdio.h>
main()/* Program introduces the for statement, counts to ten */
{
int count;
for( count = 1; count <= 10; count = count + 1 )
printf("%d ", count );
printf("\n");
}
The program declares an integer variable count. The first part of the for statement for( count = 1; initialises the value of count to 1. The for loop continues whilst the condition count <= 10; evaluates as TRUE. As the variable count has just been initialised to 1, this condition is TRUE and so the program statement printf("%d ", count ); is executed, which prints the value of count to the screen, followed by a space character. Next, the remaining statement of the for is executed
count = count + 1 );
which adds one to the current value of count. Control now passes back to the conditional test, count <= 10;
which evaluates as true, so the program statement printf("%d ", count );
is executed. Count is incremented again, the condition re-evaluated etc, until count reaches a value of 11.
When this occurs, the conditional test
count <= 10;
evaluates as FALSE, and the for loop terminates, and program control passes to the statement
printf("\n");
which prints a newline, and then the program terminates, as there are no more statements left to execute.
THE WHILE STATEMENT
The while provides a mechanism for repeating C statements whilst a condition is true. Its format is,
while( condition )
program statement;
Somewhere within the body of the while loop a statement must alter the value of the condition to allow the loop to finish.
Example:
/* Sample program including while */
#include <stdio.h>
main()
{
int loop = 0;
while( loop <= 10 ) {
printf("%d\n", loop);
++loop;
}
}
The above program uses a while loop to repeat the statements printf("%d\n", loop);
++loop;
whilst the value of the variable loop is less than or equal to 10.
Note how the variable upon which the while is dependant is initialised prior to the while statement (in this case the previous line), and also that the value of the variable is altered within the loop, so that eventually the conditional test will succeed and the while loop will terminate. This program is functionally equivalent to the earlier for program which counted to ten.
THE DO WHILE STATEMENT
The do { } while statement allows a loop to continue whilst a condition evaluates as TRUE (non- zero). The loop is executed as least once.
Example:
/* Demonstration of DO...WHILE*/
#include <stdio.h>
main()
{
int value, r_digit;
printf("Enter the number to be reversed.\n");
scanf("%d", &value);
do
{
r_digit = value % 10;
printf("%d",r_digit);value=value/10;
} while(value!=0); printf("\n");
}
The above program reverses a number that is entered by the user. It does this by using the modulus
% operator to extract the right most digit into the variable r_digit. The original number is then divided by 10, and the operation repeated whilst the number is not equal to 0.
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