Notes

TASK 2
#include <iostream>
#include <pthread.h>
#include <stdio.h>
using namespace std;
int a[100];
int sum[4];
signed int div= -1;
int i;

void* sum_array(void* arg){
div += 1;//variable to make 4 divisions of array

for (int i=div*25; i < (div+1)*25; i++){//dividing arrays in 4 parts because 4 threads
sum[div] += a[i];}//calculating sum of 4 different divisions
//storing them in sum[] array
}

int main(){
int total_sum=0; //variable to store the total_sum of 4 divisionals sums

for (int i=0; i<100; i++){
a[i]=1;} //assuming all 100 elements are 1 hardcoded filling the array

pthread_t threads[4]; // initialize 4 threads

for (int i=0; i< 4; i++){
pthread_create(&threads[i], NULL, sum_array, (void*)NULL);}//creating 4 threads

for(int i=0; i< 4; i++){
pthread_join(threads[i], NULL);}//wait for all threads to complete

for (int i =0; i < 4; i++){
total_sum += sum[i];}//sum of all 4 divisions
cout << "sum is " <<total_sum<< endl;
return 0;}

//compile using g++ -pthread lab6.cpp
//then a.out file is made
//execute the command ./a.out