Thread: Multi-threading calculating pi with user input

Code:

#include<pthread.h>
#include<math.h>
#include<stdlib.h>
#include<unistd.h>

#define NUM_THREADS 8
int threads = 0;

typedef struct {
    int rank;
    double sum;
} thread_data;

thread_data td[NUM_THREADS];

void* help_pi(void *rank) {
    int thread_rank = *(int *)rank;
    double incr = 0;
    int sign;
        int k = thread_rank;
        

    if (k % 2) {
        sign = -1;
    } else {
        sign = 1;
    }

    td[thread_rank].sum = 4*((double)sign / (2 * thread_rank + 1));

    do {
        k += NUM_THREADS;

        if (k % 2) {
            sign = -1;
        } else {
            sign = 1;
        }

        incr = (double)sign / (2 * k + 1);
        td[thread_rank].sum += 4 * incr;
    }
  while ( fabs(incr) > 1e-6);

    return NULL;
}

int main(){
    int rank = 0;
    int err;
    double pi = 0;
    
    
    
    //Introduction
    printf("\nThe Leibniz formula is an infinite series method of calculating PI.\n");
    
    //user input
    printf("\nEnter the number of iterations: ");
    scanf("%d",&threads);
    
    pthread_t thread_ids[NUM_THREADS];

    while(rank < threads) {
        td[rank].rank = rank;

        err = pthread_create(&(thread_ids[rank]), NULL, help_pi, (void*)&td[rank].rank);
        if (err != 0) {
            printf("Can't create thread error =%d\n", err);
            return 1;
        }
        rank++;
    }

    rank = 0;
    while(rank < threads) {
        pthread_join(thread_ids[rank], NULL);
        rank++;
    }

    rank = 0;
    while(rank < threads) {
        pi += td[rank].sum;
        rank++;
    }
    //output
    printf("\nThe value of Pi = %f\n", threads, pi);

    return 0;
    }

I'm having trouble printing because it keeps telling me that the f expects argument of double but argument has two type int, not sure what to do now
thankyou