ICS 103: Computer Programming in C
Handout-07
Topic:
Control Structures (Repetition & Loop Statements)
Instructor:
M. Waheed Aslam.
Objective:
·
To know use of increment operator ++, and decrement operator
--.
·
To know syntax of wile, do-while, for statements (loops).
·
To know working of above loops with examples.
Use
of increment operator ++, and decrement operator --
i++ means i=i+1; first, initial value of i will be assigned and after that, the value
i
-- means i=i-1; of
i will be incremented / decremented accordingly
Example:
#include<stdio.h>
main()
{
int i=2, r1 ;
r1=i++;
printf("Value of r1 is :
%d", r1);
}
Sample Output: Output:
++i means i=i+1;
Here, in the first step, the initial value of i will be incremented
--
i means i=i-1; or
decremented and then the value of i will
be assigned).
Example:
#include<stdio.h>
main()
{
int i=2, r1;
r1 = ++i;
printf("Value of r1 is : %d", r1);
}
Looping Structures:
The
while statement:
Syntax: while (expression)
statement
A
conditional loop is one whose continued execution depends on the value
of a logical expression. In the above
syntax, as long as the expression is true the statement (or statements if
enclosed within braces) is executed. When the expression evaluates to false,
the execution of the statement(s) stops and program continues with the other
following statements.
Example: Let number be an integer variable.
while (number > 100)
{
printf (“Enter a number\n”);
scanf (“%d”, &number);
}
In
the above example:
·
As long as the
entered value of number is greater than 100 the loop continues to ask to enter
a value for number.
·
Once a number
less than or equal to 100 is entered it stops asking.
·
If in the
beginning itself the value of number is less than or equal to 100, then the
loop is not executed at all.
Note: In the while loop the expression is tested
before the loop body statements are entered. So, if the expression is false in
the beginning the loop body is never entered.
do…while
statement:
Syntax: do
Statement
while (expression);
Here:
·
The expression
is tested after
the statement(s) are executed.
·
So, even if
the expression is false in the beginning the loop body is entered at least once.
·
Here also like
the while statement, as long as the expression is true the statement (or
statements if enclosed within braces) is executed.
·
When the
expression evaluates to false the execution of the statement(s) stops and
program continues with the other following statements.
Example: The example of while loop can be written
with do…while loop as:
do
{ printf (“Enter a number\n”);
scanf (“%d”, &number);
}
while
(number > 100);
In
this example:
·
As long as the
entered value of number is >100 the loop continues to ask to enter a value
for number.
·
Once a number
less than or equal to 100 is entered it stops asking.
Note: In the conditional looping using while and
do…while the number of times the loop will be executed is not known at
the start of the program.
for statement:
Syntax: for (expression 1; expression 2;
expression 3)
Statement
In
the iterative looping using for
loop:
·
the number of
times the loop will be executed is known at the start of the program.
·
In the above
syntax:
§
expression 1 is the initialization statement which assigns
an initial value to the loop variable.
§
expression 2 is the testing expression where the loop
variable value is checked. If it is true
the loop body statement(s) are executed and if it is false the statements(s) are not executed.
§
expression 3 is usually an increment or decrement expression
where the value of the loop variable is incremented or decremented.
Example:
for
(count = 0 ; count < 10 ; count++)
{
printf
(“Enter a value\n”) ;
scanf (“%d”, &num) ;
num = num + 10 ;
printf (“NUM = %d\n”, num) ;
}
In
this example:
·
The integer
variable count is first initialized by assigning it the value 0.
·
Then the value of
count is checked if it is
less than 10. If it is < 10:
§
the loop body asks to enter a value for num.
§
Then the value of
count is incremented by 1 and again count is checked for less than 10:
o
If it is true
the loop body is again executed and then the count is incremented by 1
and checked for < 10.
o
It keeps on doing
like this until the count is >= 10.
Then the loop stops. So, here the loop is executed 10 times.
Note: The increment operation is written as ++ and decrement operation is
written as --. The increment
increases the value by 1 and decrement decreases the value by 1.
How
to generate number from 1 to 10 Using different loops:
|
for |
while |
do-while |
|
for(n=1; n<=10; ++n) {
------ ------ ------ } |
n=1; while(n<=10)
{ ------ ------ n=n+1; } |
n=1; do { ------ ------ n=n+1; } while (n <=10) |
Useful Solved Examples using different
loops:
Example 1: for loop:
#include<stdio.h>
void main()
{
int num, square, limit;
printf("Please Input value of limit : ");
scanf("%d",
&limit);
for (num=0; num < limit;
++num)
{
square
= num*num;
printf("%5d
%5d\n", num, square);
} // end of for
} // end of main
Example 2:
/********************************************************/
Program Showing a Sentinel-Controlled for loop to
compute
the
sum of a list of exam scores.
/********************************************************/
#include
<stdio.h>
#define
SENTINEL -99
int
main(void)
{
int sum = 0, /* sum of
scores input so far */
score;
/* current score */
printf("Enter first score (or %d to quit)>
", SENTINEL);
for(scanf("%d",
&score); score != SENTINEL; scanf("%d",
&score))
{
sum += score;
printf("Enter next
score (%d to quit)> ", SENTINEL);
} // end of for loop
printf("\nSum of exam scores is %d\n", sum);
return
(0);
} // end of main
Example 3: while loop:
/*Conditional loop Using while Statement */
#include <stdio.h>
#define RIGHT_SIZE 10
void main()
{
int diameter;
printf("Please Input Balloon's diameter >
");
scanf("%d",&diameter);
while(diameter
< RIGHT_SIZE)
{
printf("Keep blowing ! \n");
printf("Please Input new Balloon's diameter > ");
scanf("%d", &diameter);
} // end of while loop
printf("Stop blowing ! \n");
} // end of main
Example 4: do-while loop:
/* do-while loop */
#include<stdio.h>
void main()
{int num;
do
{printf("Please Input Positive numbers
between ( < 1 or >= 10 ) : ");
scanf("%d",&num);
} // end of do loop
while (num < 1 || num >=10)
;
printf("Dear
, Sorry ! Your number is out of specified
range in program");
} // end of main
Example 5: Use of Increment and
Decrement operators:
/* Explanation on Increment , Decrement operators */
#include<stdio.h>
void main()
{int n, m, p, i = 3, j = 9;
n = ++i * --j;
printf("From above First given expression calculated n=%d
i=%d j=%d\n", n, i, j);
m = i + j--;
printf("From above second given expression calculated n=%d
i=%d j=%d\n",m ,i ,j);
p = i + j;
printf("From above Third given expression calculated n=%d
i=%d j=%d\n", p, i, j);
} // end of main
