This is a C program to check if a number if prime or not
A prime number is a number which is not completely divisible by any number except 1 and itself.
If n is the number to be checked, the program will check if n is completely divisble by any number from 2 to n divided by 2
Strictly speaking the check need to be done only till the square root of n but to keep the program simple we will carry on the division until n/2
check_prime.c
/* ********************************************** * Program to check a number is Prime or not * ************************************************/ #include <stdio.h> #include <conio.h> int main() { int num, i; // Read a number printf("Enter a number : "); scanf("%d",&num); //Check if the number is divsible for (i=2; i <= num / 2; i++) { if (num % i == 0) { printf("%d is not a prime number. It is completely divisible by %d",num,i); getch(); return 0; } } printf("%d is a prime number",num); // Wait for key press getch(); return 0; }
Program Output
Enter a number : 1324801 1324801 is not a prime number. It is completely divisible by 1151
