# C Program to Check Whether a Number is Prime or Not

In this tutorial, i am going to show you how to check whether a number is prime or not with the help of 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.

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

• Algorithm to Check a Number is Prime or Not
• 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

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

Follow the below given algorithm to write a program to check a number is prime or not; as follows:

```Step 1: Start
Step 3: Set f=0
Step 4: For i=2 to n-1
Step 5: If n mod 1=0 then
Step 6: Set f=1 and break
Step 7: Loop
Step 8: If f=0 then
print 'The given number is prime'
else
print 'The given number is not prime'
Step 9: Stop```

### 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 result of the above c program; as follows:

`Please Enter any number to Check for Prime :- 1010 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 result of the above c program; as follows:

`Please Enter any number to Check for Prime :- 1111 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 result of the above c program; as follows:

`Please Enter any number to Check for Prime :- 3131 is a Prime Number`

Categories C