Question

How to find the 100001 prime number in C

Answer 1

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

// Function to check if a number is prime
bool isPrime(int num) {
    if (num <= 1) return false;
    if (num <= 3) return true;
    if (num % 2 == 0 || num % 3 == 0) return false;

    for (int i = 5; i * i <= num; i += 6) {
        if (num % i == 0 || num % (i + 2) == 0) return false;
    }

    return true;
}

int main() {
    int count = 0; // Counter for prime numbers
    int num = 1;   // Current number to check
    const int target = 100001; // Target prime number position

    while (count < target) {
        num++;
        if (isPrime(num)) {
            count++;
        }
    }

    printf("The 100,001st prime number is: %d\n", num);
    
    return 0;
}



/*
run:

The 100,001st prime number is: 1299721

*/

 

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Answer 2

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

// Function to check if a number is prime
bool isPrime(int num) {
     if (num < 2) return false;
    
    for (int i = 2; i <= sqrt(num); i++) {
        if (num % i == 0) {
            return false;
        }
    }
    
    return true;
}

int main() {
    int count = 0; // Counter for prime numbers
    int num = 1;   // Current number to check
    const int target = 100001; // Target prime number position

    while (count < target) {
        num++;
        if (isPrime(num)) {
            count++;
        }
    }

    printf("The 100,001st prime number is: %d\n", num);
    
    return 0;
}



/*
run:

The 100,001st prime number is: 1299721

*/

 

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