c - Thread program that calculates pi -


writing program class calculates pi. got coding done , program runs - values doesn't work. program supposed take in 2 parameters, 1st 1 number of elements calculate pi , second number of threads use. works flawlessly many numbers 1, 2, 5 ,6, 7, 8 , others doesn't calculate well. it's limits in loops can't figure out. appreciated. code:

#include <stdio.h> #include <stdlib.h> #include <pthread.h>  //global variables int n, t; double *vsum;  //pie function void* pie_runner(void* arg) {     long j = (long)arg;         //double *limit_ptr = (double*) arg;     //double j = *limit_ptr;      //for(int = (j-1)*n/t; < n*(j) /t; i++)     for(int = (n/t)*(j-1); < ((n/t)*(j)); i++)     {          if(i % 2 == 0){             vsum[j] += 4.0/((2*j)*(2*j+1)*(2*j+2));              //printf("vsum %lu = %f\n", j, vsum[j]);                   }         else{             vsum[j] -= 4.0/((2*j)*(2*j+1)*(2*j+2));             //printf("vsum %lu = %f\n", j, vsum[j]);                   }       }      pthread_exit(0); }  int main(int argc, char **argv) {      if(argc != 3) {         printf("error: must send 2 parameters, sent %d\n", argc-1);         exit(1);     }     n = atoi(argv[1]);     t = atoi(argv[2]);       vsum = malloc((t+1) * sizeof(*vsum));     if(vsum == null) {         fprintf(stderr, "memory allocation problem\n");         exit(1);     }      if(n <= t) {         printf("error: number of terms must greater number of threads.\n");         exit(1);         }      for(int p=1; p<=t; p++)        //initialize array 0     {         vsum[p] = 0;     }      double pie = 3.0;     //launch threads     pthread_t tids[t+1];      for(long = 1; i<=t; i++)     {         pthread_attr_t attr;         pthread_attr_init(&attr);         pthread_create(&tids[i], &attr, pie_runner, (void*)i);     }      //wait threads...     for(int k = 1; k<=t; k++)     {         pthread_join(tids[k], null);     }      for(int x=1; x<=t; x++)     {         pie += vsum[x];     }      printf("pi computed %d terms in %d threads %.20f\n", n, t, pie);      //printf("pi computed %d terms in %d threads %20f\n", n, t, pie);      free(vsum); }

values not working:

 ./pie1 2 1 pi computed 2 terms in 1 threads 3.00000000000000000000 ./pie1 3 1 pi computed 3 terms in 1 threads 3.16666666666666651864  ./pie1 3 2 pi computed 3 terms in 2 threads 3.13333333333333330373  ./pie1 4 2 pi computed 4 terms in 2 threads 3.00000000000000000000  ./pie1 4 1 pi computed 4 terms in 1 threads 3.00000000000000000000  ./pie1 4 3 pi computed 4 terms in 3 threads 3.14523809523809516620  ./pie1 10 1 pi computed 10 terms in 1 threads 3.00000000000000000000  ./pie1 10 2 pi computed 10 terms in 2 threads 3.13333333333333330373  ./pie1 10 3 pi computed 10 terms in 3 threads 3.14523809523809516620  ./pie1 10 4 pi computed 10 terms in 4 threads 3.00000000000000000000 ./pie1 10 5 pi computed 10 terms in 5 threads 3.00000000000000000000 ./pie1 10 6 pi computed 10 terms in 6 threads 3.14088134088134074418  ./pie1 10 7 pi computed 10 terms in 7 threads 3.14207181707181693042 ./pie1 10 8 pi computed 10 terms in 8 threads 3.14125482360776464574  ./pie1 10 9 pi computed 10 terms in 9 threads 3.14183961892940200045 ./pie1 11 2 pi computed 11 terms in 2 threads 3.13333333333333330373  ./pie1 11 4 pi computed 11 terms in 4 threads 3.00000000000000000000

i think problem used expression n/t in code. here n , t integers. c language (and many others) treat integer dividion not same way hand.

for example, 5/3 = 1, not 1.66667. 1.66667, can cast 1 of integer double.


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