multithreading - not understanding a part of code -


hi not understanding part of code in threads program , code 

int niza[1000]; pthread_t threads[6];  void *popolni(void* n) {     int counter=*(int *)n;     for(int i=0;i<n;i++)         niza[i]=rand()%counter;     pthread_exit(null); }  void *promeni(void* id) {     int threadid=*(int *)id,dolzina=strlen(niza);     int del=round(dolzina/4);     for(int i=(id-1)*del;i<id*del;i++)         niza[i]+=niza[i]/2;     pthread_exit(null); }  void *pecati(void* n) {     int counter=*(int *)n;     for(int i=0;i<counter;i++)         printf("%d ",niza[i]);     pthread_exit(null); }  int main(int argc, char* argv[]) {     srand(time(null));     int n;     scanf("%d",&n);     pthread_create(&threads[0],null,popolni,(void *)&n);     pthread_join(threads[0],&status);     for(int i=1;i<5;i++)         pthread_create(&threads[i],null,promeni,(void *)&i);     for(int i=1;i<5;i++)         pthread_join(threads[i],&status);     pthread_create(&threads[5],null,pecati,(void *)&n);     pthread_join(threads[5],&status);     return 0; }`

the part don't understand this

for(int i=(id-1)*del;i<id*del;i++)         niza[i]+=niza[i]/2;

the first thread has fill array , second 4 threads have split on 4 parts , fill array . me?


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