How to specify the number of threads I want to use? - c

Question

I am trying to Multiply the matrix with use of threads. The code seems to be working. I just need to know how to specify the number of threads so that I can count how much time it's taking. I want to create a table of threads and time it's taking to compute the matrix.
I am dynamically allocating the matrix and filling it with random numbers.
I am creating threads to compute the resultant matrix.
C Program to multiply two matrix using pthreads without use of global variables
#include<stdio.h>
#include<pthread.h>
#include<unistd.h>
#include<stdlib.h>
//Each thread computes single element in the resultant matrix
void *mult(void* arg)
{
int *data = (int *)arg;
int k = 0, i = 0;
int x = data[0];
for (i = 1; i <= x; i++)
k += data[i]*data[i+x];
int *p = (int*)malloc(sizeof(int));
*p = k;
//Used to terminate a thread and the return value is passed as a pointer
pthread_exit(p);
}
//Driver code
int main()
{
int i, j, k, row1, col1, row2, col2, r, sum;
printf("Enter the number of rows for matrix 1\n");
scanf("%d",&row1);
printf("Enter the number of columns for matrix 1 \n");
scanf("%d",&col1);
printf("Enter the number of rows for matrix 2 \n");
scanf("%d",&row2);
printf("Enter the number of columns for matrix 2\n");
scanf("%d",&col2);
int **a = (int **) malloc(row1 * sizeof(int *));
for(i=0;i<row1;i++)
a[i] = (int *) malloc(col1 * sizeof(int));
int **b = (int **) malloc(row2 * sizeof(int *));
for(i=0;i<row2;i++)
b[i] = (int *) malloc(col2 * sizeof(int));
for(i=0;i<row1;i++)
{
for(j=0;j<col1;j++)
{
a[i][j] = (rand()%9) + 1;
}
}
for(i=0;i<row2;i++)
{
for(j=0;j<col2;j++)
{
b[i][j] = (rand()%9) +1;
}
}
int N = row1*col2;
//declaring array of threads of size row1*col2
pthread_t *threads;
threads = (pthread_t*)malloc(N*sizeof(pthread_t));
int count = 0;
int* data = NULL;
for (i = 0; i < row1; i++)
for (j = 0; j < col2; j++)
{
//storing row and column elements in data
data = (int *)malloc((N)*sizeof(int));
data[0] = col1;
for (k = 0; k < col1; k++)
data[k+1] = a[i][k];
for (k = 0; k < row2; k++)
data[k+col1+1] = b[k][j];
//creating threads
pthread_create(&threads[count++], NULL,
mult, (void*)(data));
}
printf("RESULTANT MATRIX IS :- \n");
for (i = 0; i < N; i++)
{
void *k;
//Joining all threads and collecting return value
pthread_join(threads[i], &k);
int *p = (int *)k;
printf("%d ",*p);
if ((i + 1) % col2 == 0)
printf("\n");
}
return 0;
}