How to find prime number in C

 A prime number is a positive integer greater than 1 that has no positive integer divisors other than 1 and itself. To check if a number is prime or not in C, you can use a simple program that iterates through potential divisors and checks if the number is divisible by any of them. Here's a basic C program to determine if a number is prime:

c
#include <stdio.h>
int isPrime(int num) 
{ 
    if (num <= 1) 
    { 
        return 0; // 0 and 1 are not prime numbers 
     }
    for (int i = 2; i * i <= num; i++) 
    { 
    if (num % i == 0) 
    { 
        return 0; // If num is divisible by any number from 2 to sqrt(num), it's not prime
        }
     }
    return 1; // If no divisors were found, it's a prime number 
} 
int main() 
{ 
    int num; 
    printf("Enter a positive integer: "); 
    scanf("%d", &num); 
    if (isPrime(num)) 
    { 
        printf("%d is a prime number.\n", num); 
    } 
    else 
    { 
        printf("%d is not a prime number.\n", num); 
    } 
    return 0; 
}

In this program:

1. The isPrime function takes an integer num as input and returns 1 if it's prime and 0 if it's not.

2. Inside the isPrime function:

• If num is less than or equal to 1, it immediately returns 0 because 0 and 1 are not prime numbers.
  
• It iterates from 2 to the square root of num using a for loop.
  
• Within the loop, it checks if num is divisible by the current i. If it is, it returns 0 because a divisor was found.
  
• If no divisors are found in the loop, it returns 1, indicating that num is prime.

In the main function:

• The user is prompted to enter a positive integer.
• The isPrime function is called to determine if the input number is prime or not.
• The result is printed to the console.
• When you run the program, it will tell you whether the entered number is prime or not