For Loop - O Level (NIELIT)

for and while Loops

Looping statement are the statements execute one or more statement repeatedly several number of times. In C programming language there are three types of loops:

For loop
While loop
Do while loop

FOR Loop:

for loop is a statement which allows code to be repeatedly executed. For loop contains 3 parts Initialization, Condition and Increment or Decrements.

Syntax:

for(initial value ;condition; increment/decrement)

{

statement 1

……………

statement n

}

Variation in FOR Loop

A for loop can have multiple variations that makes more flexible and efficient.

Multiple initialization and update expression
Optional expression
Infinite loop
Empty loop

Multiple initialization and update expression

A for loop may contain multiple initialization and update expressions. The multiple expressions must be separated by commas.

Example:

int i,j;
for(i=1,j=20; I,=10; i++,j--)
{
	printf("%d %d ",i,j)
}

Optional Expression

By now you are familiar that a for loop contains three types of expressions: initialization expression(condition) and an update expression. But, all these expressions are optional, i.e., we can skip any or all of these expressions depending upon the requirement of the program.

Case 1:

int i=2;
for( ;i<=20;i=i+2)
{
    printf("%d",i);
}

Case 2:

int i=2;
for( ;i<=20; )
{
    printf(“%d”,i);
    i=i+2;
}

Case 3:

int i=2;
for( ; ; )
{
	printf(“%d”,i);
	i=i+2;
	if(i>20)
	{
		break;
	}
}

Infinite Loop

A for loop will execute its statement block infinite number of times if we skip the condition. If the test expression (condition) is not present in the loop, it will never return false. Hence, it will execute endlessly and become an infinite loop.

Case 1

int I
for(i=1; ;i++)
{
     pritlf("%d",i);
}

Case 2

int i;
for( ; ; )
{
   pritlf("%d",i);
}

Case 3

int i;
for(i=1;i<=i;i++)
{
   pritlf("%d",i);
}

Here , i<=I will always be true.

Empty Loop

A loop without any statement in its body is called an empty loop

Case 1:

int i
for(i=2;i<=50;i++)
{
}

Case 2:

for(i=2;i<=50;i++);

Qus. 1 : Which code will print k 20 times?

for (i=1; i < 20; i++) printf ("k");
for (i=1; i = 20; i++) printf ("k");
for (i=0; i < 20; i++) printf ("k");
for (i=0; i <= 20; i++) printf ("k");

Qus. 2 : What is the final value of x when the code is executed?<pre>int x; for(x=0; x<10; x++) {} </pre>

Qus. 3 : The following code ‘for(;;)’ represents an infinite loop. It can be terminated by.

break
exit(0)
abort()
All of the mentioned

Qus. 4 : What will be the output of following program? <pre>int main() { for(int c=1;c<5;++c); printf(“%d”,c); }</pre>

1
5
6
12345

Qus. 5 : Which of the following is the correct syntax for a for loop in C?

for (int i = 0; i < 10; i++)
for i = 0 to 10 step 1
for (i = 0; i < 10; i++)
for (i < 10; i++)

Qus. 6 : How many times will the following loop execute?<pre>int j; for(j = 1; j <= 10; j = j-1) printf("INFOMAX");</pre>

Forever
Never
0
10

Programs

C Program to Calculate the Sum of Natural Numbers