C Program - Print Prime Numbers From 1 to N

Print Primes Using Nested Loops

#include <stdio.h>
int main() {
    int N, i, j, isPrime;
    printf("Enter the upper limit: ");
    scanf("%d", &N);
    printf("Prime numbers between 1 and %d are: ", N);
    for (i = 2; i <= N; i++) {
        isPrime = 1;
        for (j = 2; j < i; j++) {
            if (i % j == 0) {
                isPrime = 0;
                break;
            }
        }
        if (isPrime) {
            printf("%d ", i);
        }
    }
    printf("\n");
    return 0;
}

Enter the upper limit: 10
Prime numbers between 1 and 10 are: 2 3 5 7

This straightforward approach checks each number from 2 up to the entered limit by dividing it by every smaller integer. If none divide evenly, the number is printed as prime.

Print Primes Using Optimized Check

#include <stdio.h>
#include <math.h>
int isPrime(int num) {
    int i;
    if (num <= 1) return 0;
    if (num == 2) return 1;
    if (num % 2 == 0) return 0;
    for (i = 3; i <= sqrt(num); i += 2) {
        if (num % i == 0) return 0;
    }
    return 1;
}
int main() {
    int N, i;
    printf("Enter the upper limit: ");
    scanf("%d", &N);
    printf("Prime numbers between 1 and %d are: ", N);
    for (i = 2; i <= N; i++) {
        if (isPrime(i)) {
            printf("%d ", i);
        }
    }
    printf("\n");
    return 0;
}

Enter the upper limit: 20
Prime numbers between 1 and 20 are: 2 3 5 7 11 13 17 19

An optimized approach uses a helper function that checks divisibility only up to the square root of a number and skips even numbers after 2. Each number from 2 to N is tested with this function before being printed.

C Program – Print Prime Numbers From 1 to N - Nested Loops & Optimized Check

Print Primes Using Nested Loops

Print Primes Using Optimized Check

Comments

C Control Flow❯

C Program – Print Prime Numbers From 1 to N - Nested Loops & Optimized Check

Print Primes Using Nested Loops

Print Primes Using Optimized Check

Comments

C Control Flow❯

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