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

## Write a Program to check Prime or Not in C

``````
Program in C to Check Prime Number from all the natural number given.

#include <stdio.h>
int prime(int);
int natural(int n)           \\ Natural number function
{

if  (n==1)
{     return 1;}
natural(n-1);
prime(n);
}
int   prime(int    n) {           \\ prime number function
int   i,flag=0;
for(i=2;i<=n/2;i++)
{
if(n%i==0)
{
flag=1;
break;
}
}
if(n==1)
{
printf("\n%d is Neither Prime nor Composite",n);
}
else{
if(flag==0)
{
printf("\n%d  is Prime. ",n);
}
else
{
printf("\n%d  Non Prime",n);
}
}

}

int main()
{
int n=25;          \\ check prime number until 25.
natural(n);        \\ call function natural()

return 0;
}

``````

Output :

``````
2  is Prime.
3  is Prime.
4  Non Prime
5  is Prime.
6  Non Prime
7  is Prime.
8  Non Prime
9  Non Prime
10  Non Prime
11  is Prime.
12  Non Prime
13  is Prime.
14  Non Prime
15  Non Prime
16  Non Prime
17  is Prime.
18  Non Prime
19  is Prime.
20  Non Prime
21  Non Prime
22  Non Prime
23  is Prime.
24  Non Prime
25  Non Prime              ``````

## Write a Program in C to Check Given Number is Prime or Not.

``````Program to Check Prime Number taking input from user

#include <stdio.h>
int prime(int);

int   prime(int    n) {
int   i,flag=0;
for(i=2;i<=n/2;i++)
{
if(n%i==0)
{
flag=1;
break;
}
}
if(n==1)
{
printf("\n%d is Neither Prime nor Composite",n);
}
else{
if(flag==0)
{
printf("\n%d  is Prime. ",n);
}
else
{
printf("\n%d  Non Prime",n);
}
}

}

int main()
{
int n;
printf("Enter an integer: ");
scanf("%d", &n);
printf("Number = %d",n);

prime(n);

return 0;
}
``````

Output :

``````
Enter an integer: 5
Number = 5
5  is Prime.
``````

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