4 Loops in C

Loops in C Programming
Types of Loops in C
There are three main types:

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

 
for Loop
The for loop is used when the number of iterations is known in advance.
Syntax
for(initialization; condition; increment/decrement)
{
statements;
}
Flow

1. Initialization executes once
2. Condition is checked
3. Loop body executes
4. Increment/decrement happens
5. Steps repeat until condition becomes false

Example
#include <stdio.h>
int main()
{
int i;
for(i = 1; i <= 5; i++)
{
printf(“%d\n”, i);
}
return 0;
}
Output:
1
2
3
4
5
 
while Loop
The while loop is used when the number of iterations is not known beforehand.
The loop continues as long as the condition is true.
Syntax
while(condition)
{
statements;
}
Example
#include <stdio.h>
int main()
{
int i = 1;
while(i <= 5)
{
printf(“%d\n”, i);
i++;
}
return 0;
}
 
do–while Loop
The do–while loop executes the body at least once, even if the condition is false.
This is called an exit-controlled loop.
Syntax
do
{
statements;
}
while(condition);
Example
#include <stdio.h>
int main()
{
int i = 1;
do
{
printf(“%d\n”, i);
i++;
}
while(i <= 5);
return 0;
}
Difference Between while and do–while

while Loop	do–while Loop
Condition checked before execution	Condition checked after execution
May execute zero times	Executes at least once
Entry-controlled loop	Exit-controlled loop

 
Nested Loops
A loop inside another loop is called a nested loop.
Example
#include <stdio.h>
int main()
{
int i, j;
for(i = 1; i <= 3; i++)
{
for(j = 1; j <= 3; j++)
{
printf(“* “);
}
printf(“\n”);
}
return 0;
}
Output:
* * *
* * *
* * *
 
Loop Control Statements
break Statement
Used to exit the loop immediately.
for(i = 1; i <= 10; i++)
{
if(i == 5)
break;
printf(“%d”, i);
}
 
continue Statement
Used to skip the current iteration and move to the next.
for(i = 1; i <= 5; i++)
{
if(i == 3)
continue;
printf(“%d”, i);
}
 
Differences Between break, continue, and goto

Feature	break	continue	goto
Purpose	Exits a loop or switch block	Skips the current iteration	Transfers control to a label
Scope	Nearest enclosing loop or switch	Nearest enclosing loop	Any labeled state- ment in the same function
Use Case	Terminating loops or switch	Skipping      specific iterations	Exiting deeply nested loops
Readability	Generally safe and readable	Generally safe and readable	Can     make    code harder to read

 
Important Points to Remember
Infinite loop occurs when condition never becomes false
Semicolon after loop condition can create errors
Use proper initialization and increment
for(;;) creates an infinite loop
Example:
for(;;)
{
printf(“Infinite Loop”);
}
 
Practice Programs

1. Print Numbers from 1 to 10

for(int i = 1; i <= 10; i++)
printf(“%d “, i);
 

2. Sum of First N Numbers

int n, i, sum = 0;
scanf(“%d”, &n);
for(i = 1; i <= n; i++)
sum = sum + i;
printf(“Sum = %d”, sum);
 

3. Multiplication Table

int num, i;
scanf(“%d”, &num);
for(i = 1; i <= 10; i++)
printf(“%d x %d = %d\n”, num, i, num*i);