Question

Modify the code below to implement the program that will sum up 1000 numbers using 5 threads.

1st thread will sum up numbers from 1-200

2nd thread will sum up numbers from 201 - 400

...

5th thread will sum up numbers from 801 - 1000

Make main thread wait for other threads to finish execution and sum up all the results.

Display the total to the user.

#include <pthread.h>

#include <stdio.h>

#include <stdlib.h>

#define N_OF_THREADS 4
void * print(void *tid){

printf("Hello %d\n", tid); pthread_exit(NULL);
}
int main(){

pthread_t threads[N_OF_THREADS];

int status, i; //

printf("Main. Creating thread %d\n", i);

for (int i=0; i<N_OF_THREADS; i++) {    

printf("Main. Creating thread %d\n", i);

status = pthread_create(&threads[i], NULL, print, (void*)i);

if(status){

printf("Error %d\n", status);

exit(-1);

}

}

exit(NULL);

}

Answer 1

#include <pthread.h>

#include <stdio.h>

#include <stdlib.h>
#define N_OF_THREADS 4

int start_num = 0;

int sum[4] ={0};

void * print(void *tid){

printf("Hello %d\n", tid); pthread_exit(NULL);
}

void *sum_of_num(void* arg){

int thread_num = start_num++

for(int i=(thread_num*200)+1;i<=(thread_num+1)*200;i++){

     sum[start_num]+=i;

}

}

int main(){

pthread_t threads[N_OF_THREADS];

int status, i; //

printf("Main. Creating thread %d\n", i);

for (int i=0; i<N_OF_THREADS; i++) {    

printf("Main. Creating thread %d\n", i);

status = pthread_create(&threads[i], NULL, sum_of_num, (void*)i);

for (int i = 0; i < N_OF_THREADS; i++)

        pthread_join(threads[i], NULL);

int tsum = 0;

for (int i = 0; i < N_OF_THREADS; i++)

    tsum += sum[i];

printf("Total is : %d",tsum);

if(status){

printf("Error %d\n", status);

exit(-1);

}

}

exit(NULL);

}