C program to check whether a number is prime or not; Through this tutorial, we will learn how to check whether a number is prime or not using for loop, while loop, and function.

A number that’s only divisible by 1 and itself is named a Prime Number. For Example, 3, 5, 7, 11 are Prime Numbers.

**Algorithm to Check a Number is Prime or Not**

Use the following algorithm to write a program to check a number is prime or not; as follows:

Step 1:StartStep 2:Read numbernStep 3:Set f=0Step 4:For i=2 to n-1Step 5:If n mod 1=0 thenStep 6:Set f=1 and breakStep 7:LoopStep 8:If f=0 then print 'The given number is prime' else print 'The given number is not prime'Step 9:Stop

## Programs to Check Whether a Number is Prime or Not in C

- C Program to Check Prime Number Using For Loop
- C Program to Check Prime Number Using While Loop
- C Program to Check Prime Number Using Function

### C Program to Check Prime Number Using For Loop

```
#include <stdio.h>
int main()
{
int i, Number, count = 0;
printf("\n Please Enter any number to Check for Prime :- ");
scanf("%d", &Number);
for (i = 2; i <= Number/2; i++)
{
if(Number%i == 0)
{
count++;
break;
}
}
if(count == 0 && Number != 1 )
{
printf("\n %d is a Prime Number", Number);
}
else
{
printf("\n %d is Not a Prime Number", Number);
}
return 0;
}
```

**The output of the above c program; as follows:**

Please Enter any number to Check for Prime :- 10

10 is Not a Prime Number

### C Program to Check Prime Number Using While Loop

```
#include <stdio.h>
int main()
{
int i = 2, Number, count = 0;
printf("\n Please Enter any number to Check for Prime :- ");
scanf("%d", &Number);
while(i <= Number/2)
{
if(Number%i == 0)
{
count++;
break;
}
i++;
}
if(count == 0 && Number != 1 )
{
printf("\n %d is a Prime Number", Number);
}
else
{
printf("\n %d is Not a Prime Number", Number);
}
return 0;
}
```

**The output of the above c program; as follows:**

Please Enter any number to Check for Prime :- 11

11 is a Prime Number

### C Program to Check Prime Number Using Function

```
#include <stdio.h>
int Find_Factors(int Number)
{
int i, Count = 0;
for (i = 2; i <= Number/2; i++)
{
if(Number%i == 0)
{
Count++;
}
}
return Count;
}
int main()
{
int Number, count = 0;
printf("\n Please Enter any number to Check for Prime :- ");
scanf("%d", &Number);
count = Find_Factors(Number);
if(count == 0 && Number != 1 )
{
printf("\n %d is a Prime Number", Number);
}
else
{
printf("\n %d is Not a Prime Number", Number);
}
return 0;
}
```

**The output of the above c program; as follows:**

Please Enter any number to Check for Prime :- 31

31 is a Prime Number