A prime number is the number which can be exactly divided by only 1 and the number itself. For example, 11 can only be exactly divided by 1 and the number itself, so 11 is a prime number. But 14 can be divided by 1, 2, 7 and 14 so it is not a prime number but a composite number.

C program to check whether a number is prime or composite is shown below.

#include<stdio.h> int main() { int i,n,c=0; printf ("Enter a number n"); scanf ("%d",&n); for (i=1;i<=n;i++) { if(n%i==0) c=c+1; } if (c==2) printf ("The number is PRIME"); else printf ("The number is COMPOSITE"); return 0; }

Here, the number entered by the user is stored in variable *n*. The loop goes on from 1 to the number itself and inside the loop, the number is divided by *i* (*i* starts from 1 and increases by 1 in each loop). If the number is exactly divisible by *i* then the value of *c* is incremented by 1. Then, if the value of *c* is 2, it means that the number is divisible by only 2 numbers (i.e. 1 and the number itself) so the entered number is a prime number. Otherwise, it is a composite number.

**Output:**

Enter a number 5 The number is PRIME

Enter a number 10 The number is COMPOSITE