Prime Number Program In C

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Any whole number which is greater than 1 and has only two factors that is 1 and the number itself, is called a prime number. Other than these two number it has no positive divisor. For example −

7 = 1 × 7

Few prime number are − 1, 2, 3, 5 , 7, 11 etc.

Algorithm

Algorithm of this program is very easy −

START
   Step 1 → Take integer variable A
   Step 2 → Divide the variable A with (A-1 to 2)
   Step 3 → If A is divisible by any value (A-1 to 2) it is not prime
   Step 4 → Else it is prime
STOP

Pseudocode

We can draft a pseudocode of the above algorithm as follows −

procedure prime_number : number
   
   FOR loop = 2 to number - 1
      check if number is divisible by loop
      
      IF divisible
         RETURN "NOT PRIME"
      END IF
         
   END FOR
   
   RETURN "PRIME"

end procedure

Implementation

Implementation of this algorithm is given below −

#include <stdio.h>

int main() { 
   int loop, number;
   int prime = 1;
   
   number = 11;

   for(loop = 2; loop < number; loop++) {
      if((number % loop) == 0) {
         prime = 0;
      }
   }

   if (prime == 1)
      printf("%d is prime number.", number);
   else
      printf("%d is not a prime number.", number);
   return 0;
}

Output

Output of the program should be −

11 is prime number.