#include <iostream>
#include <unistd.h>
using namespace std;

int main()
{
    
    int fd[2];
    //fd[0] - read
    //fd[1] -write
    //declare all the variables
    int n;
    int countN;
    int arr[3];
    //prompt for the numbers called n
    //there are at most 3 nums(use countN to check)
    while(countN <= 2){
        cin >> n;
        // checked whether the num is from range 1 to 15
        if(n >= 1 && n <= 15)
        {
        //if yes, then push the num to array called arr
          arr[countN] = n;
          countN++;
        }
        else
        {
            //if no, then only increase the countN so that we dont cin more than 3 nums
            countN++;
        }
    }

    //print all the nums in the array named arr
    for(int i = 0; i < 3; i++)
    {
        cout << arr[i];
    }

    //initializes fork
    pid_t c_pid = fork();
    //everything belows this gonna gets executed twice

    return 0;
}

So, I am trying to initialize the fork system call, but then it has the error:

In function ‘int main()’: ‘fork’ was not declared in this scope. Can someone tell me what I have done wrong since I have check to make sure the fork initialization is not within any block like if or while loop.

I have even tried to declare it in the first line of the code(after main()), but it still has that error.