Repitition & loop control statements

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Control Structures

Repitition & loop control statements

This type of statements helps the computer to execute a group of statements repeatedly.

This allows a set of instruction to be performed until a certain condition is reached.

There are three types of loops in C:

1. for loop
2. while loop
3. do-while loop

The for loop

There are three parts of for loop:

a)counter initialization.
b)check condition
c)modification of counter.

Syntax:
for (variable initialize; check condition; modify counter)

{
statements 1;
———–;
———–;
statements n;
}

Explanation:

1. The initialization is usually an assignment that is used to set the loop control variable.

2. The condition is a relational expression that determines when the loop will exit.

3. The modify counter defines how loop control variables will change each time the loop is repeated.

These three sections are separated by semicolon (;).

The for loop is executed as long as the condition is true. When, the condition becomes false the programe execution will resume on the statement following the block.

Advantage of for loop over other loops:

All three parts of for loop (i.e. counter initialization, check condition, modification of counter) are implemented on a single line.
A structure image of for loop >
An example program to print a message 5 times using for loop:
Out put of the program
Explanation of the program:
The o/p will be in the loop 1 time, 2times till 5 times.
Something more about for loop:
1. for (p=1,n=2;n<17;n++):- we can assign multiple variable together in for loop.
2. for (n=1,m=50;n<=m;n=n+1,m=m-1):-The increment section may also have more than one part as given.
3. for (i=1,sum=0;i<20&&sum<100;++i):-The test condition may have any compound relation as given.
4. for (x=(m+n)/2;x>0;x=x/2):-It is also permissible to use expressions in the assignment statements of initialization and increment section as given.
5. for (;m!=100;):-we can omitted the initialization and increment section to set up time delay.
while loop
It is a primitive type looping control because it repeats the loop a fixed no. of time. It is also called entry controlled loop statements.
Syntax:
while (test_condition)
{
body of loop
}
Explanation:
The test condition is evaluated if the condition is true, the body of loop will be executed.
A structure image of while >
An example of program to print the number 1 to 10 using while loop:
Out put of the program
The do-while loop
The minor Difference between the working of while and do-while loop is the place where the condition is tested.
The while tests the condition before executing any of the statements within the while loop
As against this, the do-while loop tests the condition after having executed the statement within the loop.
syntax:
do
{
body of loop;
}
while (test condition);
A structure image of do-while loop >
Explanation:
It first executes the body of the loop, and then evaluates the test condition. If the condition is true, the body of loop will executed again and again until the condition becomes false.
Example of program using do-while loop:
Out put of the program
Explanation of the program:
First it will print “hello there” then it will go for condition statements.