# C Program To Find Prime Number

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number. For example, 5 is prime because only 1 and 5 evenly divide it, whereas 6 is composite because it has the divisors 2 and 3 in addition to 1 and 6. [Definition from Wikipedia]

#### C Program to Find Prime Number:

```#include <stdio.h>

int main()
{
int num, i, is_prime;
printf("Enter a number: ");
scanf("%d",&num);
is_prime = 0;
if(num<2)
is_prime = 0;
else if(num == 2)
is_prime = 1;
else {
for(i=2;i <= num/2;i++) {
if(num%i==0) {
is_prime = 0;
break;
}
else
is_prime = 1;
}
}
if(is_prime == 0)
printf("The number is not Prime!");
else
printf("The number is Prime!");
return 0;
}
```

The above algorithm is little bit slower. So make this line:

```for(i=2;i <= num/2;i++)
```

to

`for(i=2;i <= (int)sqrt(num);i++)`

and include the header file math.h.
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