C++ program to display first n prime numbers has been shown here. Here n is a positive integer. For example if n = 5, we get first 5 prime numbers i.e. 2, 3, 5, 7, 11.

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1. Program & Output

## 1. C++ Program & output to display first N prime numbers

Code has been copied
/**********************
alphabetacoder.com
C++ program to display
first N prime numbers
***********************/

#include <iostream>
#include <cmath>

using namespace std;

// function to check prime
int check_prime(int num) {
// declare variables
int i;
// 1 is not prime
if (num == 1)
return 0;
// check divisibility of num
for (i = 2; i <= sqrt(num); i++) {
if (num % i == 0) {
return 0; // num is composite so return false
}
}
// num is prime so return true
return 1;
}

int main() {
// declare variables
int n, num, count;

// take input of the number
cout << "Enter the no. of primes = ";
cin >> n;

// initialize
num = 1;
count = 0;

cout << "First " << n << " primes: ";
// find n number of primes
while (count < n) {
// check if current number is prime
if (check_prime(num)) {
cout << num << " ";
count++; // increment counter
}
num++; // increment number
}

return 0;
}


Output

Case 1:

Enter the no. of primes = 5

First 5 primes: 2 3 5 7 11

Case 2:

Enter the no. of primes = 20

First 20 primes: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71