C Program to Display Prime Numbers Between Intervals

// C Program to Display Prime
// Numbers Between Intervals
#include <stdbool.h>
#include <stdio.h>

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

    // Run a loop from 2 to square root of n.
    for (int i = 2; i * i <= n; i++) {
        // if the number is divisible by i, then n is not a
        // prime number.
        if (n % i == 0)
            return false;
    }
    // otherwise, n is prime number.
    return true;
}

// Driver code
int main()
{
    // lower value of interval
    int a = 1;

    // upper value of interval
    int b = 10;

    // Print display message
    printf("Prime numbers between %d and %d are: ", a, b);

    // Traverse each number in the interval
    // with the help of for loop
    for (int i = a; i <= b; i++) {
        // If the number is prime print it
        if (isPrime(i))
            printf("%d ", i);
    }

    return 0;
}

// This code is contributed by Susobhan Akhuli

// C program to find the prime numbers
// between a given interval using Sieve of Eratosthenes
#include <stdbool.h>
#include <stdio.h>
#include <string.h>

void SieveOfEratosthenes(int srt, int n)
{
    // Create a boolean array "prime[srt to n]" and
    // initialize all entries it as true. A value in
    // prime[i] will finally be false if i is Not a prime,
    // else true.
    bool prime[n + 1];
    memset(prime, true, sizeof(prime));
    prime[0] = false;
    prime[1] = false;

    for (int p = 2; p * p <= n; p++) {
        // If prime[p] is not changed, then it is a prime
        if (prime[p] == true) {
            // Update all multiples of p greater than or
            // equal to the square of it numbers which are
            // multiple of p and are less than p^2 are
            // already been marked.
            for (int i = p * p; i <= n; i += p)
                prime[i] = false;
        }
    }

    // Print all prime numbers
    for (int p = srt; p <= n; p++)
        if (prime[p])
            printf("%d ", p);
}

// Driver Code
int main()
{
    int srt = 1;
    int end = 10;
    SieveOfEratosthenes(srt, end);
    return 0;
}

// This code is contributed by Susobhan Akhuli