Joining threads in a loop - Conversion error - c++

Question

So I'm trying to join threads in a for loop but it's giving me the error:
invalid conversion from 'pthread_t* {aka long unsigned int*}' to
'pthread_t {aka long unsigned int}'.
The codes are as below and any help would be greatly appreciated!
Thanks in advance!
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <stdlib.h>
#include <time.h>
#include <pthread.h>
int threadArray[10][10];
int arrayVar[2];
using namespace std;
void *calc(void *arg){
int startPoint = arrayVar[0];
int endPoint = arrayVar[1];
int newArray[10][10];
int calculated;
for (int i = startPoint ; i < endPoint; i++){
for (int j = 0; j < 10; j++){
calculated = (threadArray[i][j] * 2 + 4) * 2 + 4;
newArray[i][j] = calculated;
}
}
for (int i = startPoint; i < endPoint; i++){
for (int j = 0; j < 10; j++){
cout << newArray[i][j] << " ";
}
cout << endl;
}
return NULL;
}
int main(){
int rc;
int start = 0;
int end;
ifstream numFile;
numFile.open("numbers.txt");
if (numFile.is_open()){
for (int row = 0; row < 10; row++){
std::string line;
std::getline(numFile, line);
std::stringstream iss(line);
for (int col = 0; col < 10; col++){
std::string num;
std::getline(iss, num, ' ');
std::stringstream converter(num);
converter >> threadArray[row][col];
}
}
cout << "Original 2D Array" << endl << endl;
for (int i = 0; i < 10; i++){
for (int j = 0; j < 10; j++){
cout << threadArray[i][j] << " ";
}
cout << endl;
}
cout << endl;
}
srand (time(NULL) );
const int rowArray[3] = {1, 2, 5};
int arrayIndex = rand() % 3;
int noOfRows = (rowArray[arrayIndex]);
end = noOfRows;
int noOfThreads = 10 / noOfRows;
pthread_t threads[noOfThreads];
arrayVar[2];
cout << "2D Array Altered" << endl << endl;
for (int t = 0; t < noOfThreads; t++){
arrayVar[0] = start;
arrayVar[1] = end;
rc = pthread_create(&threads[t], NULL, calc, NULL);
start = start + noOfRows;
end = end + noOfRows;
}
for (int t = 0; t < noOfThreads; t++){
rc = pthread_join(&threads[t], NULL);
}
pthread_exit(NULL);
}

Answer 1

I think threads[t] is actually just it's pid, it's an integer and you should pass in by value
pthread_join(threads[t], NULL)