C Program to Print Prime Numbers From 1 to N

Prime numbers are positive integers greater than 1 that have exactly two factors: 1 and the number itself. This program generates and displays all prime numbers from 1 to N.

• A prime number is not divisible by any number other than 1 and itself.
• The program checks each number in the given range and prints it if it is prime.

Illustration

For N = 50, the program checks every number from 1 to 50 and prints the prime numbers:

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

Approach

• Iterate through all numbers from 1 to N.
• For each number, check whether it is prime.
• In isPrime(), return false for numbers less than 2.
• Check divisibility from 2 to √n.
• If any value divides n completely, the number is not prime.
• Otherwise, print the number.

Example: Program to Print Prime Numbers From 1 to N

#include <stdbool.h>
#include <stdio.h>
#include <math.h>

// This function is to check
// if a given number is prime
bool isPrime(int n)
{
    // 0 and 1 are not prime numbers
    if (n == 1 || n == 0)
        return false;

    // Check for divisibility from 2 to sqrt(n)
    for (int i = 2; i <= sqrt(n); i++) {
        if (n % i == 0)
            return false;
    }
    return true;
}

// Driver code
int main()
{
    int N = 50;

    // Check every number from 1 to N
    for (int i = 1; i <= N; i++) {
        if (isPrime(i)) {
            printf("%d ", i);
        }
    }

    return 0;
}

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 

Explanation: The program checks every number from 1 to N using isPrime(). For each number, divisibility is tested up to its square root; if no divisor is found, the number is printed as prime.