Question

How to find the 100001 prime number in C++

Answer 1

#include <iostream>

// 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++;
        }
    }
 
    std::cout << "The 100,001st prime number is: " << num << std::endl;
}
 
  
  
/*
run:
 
The 100,001st prime number is: 1299721
  
*/

 

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Answer 2

#include <iostream>
#include <cmath>

// 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++;
        }
    }
 
    std::cout << "The 100,001st prime number is: " << num << std::endl;
}
 
  
  
/*
run:
 
The 100,001st prime number is: 1299721
  
*/

 

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