C fork and pipe add numbers from a file - c

Question

Totals different for same file when executed.
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAX_FILE_NAME 100
#define RUNS 1
int main() {
int num,i;
FILE *fp;
char*s, buf[1024];
int count =0;
char c;
char filename[MAX_FILE_NAME];
printf("Enter filename: ");
scanf ("%s",filename);
if ((fp =fopen(filename, "r")) == NULL) {
printf("Error");
exit(1);
}
fscanf(fp,"%d",&num);
for (c = getc(fp); c!= EOF; c = getc(fp))
{
if (c == '\n'){
count = count+1;
}
}
printf("%s has %d numbers \n", filename, count);
int f;
printf("Choose from the options how many processes you want to use [1,2,4]: ");
scanf("%i", &f);
printf("%i processes \n", f);
int fds[f+1][2];
int numb[count];
int x,k;
time_t start, finish;
start = time(NULL);
for(i = 0; i < RUNS; i++)
{
pipe(fds[f]);
for( x = 0; x<f; x++)
{
pipe(fds[x]);
int ind[2];
ind[0] = ((x)*(count/f));
ind[1] = ((x+1)*(count/f));
write(fds[x][1], &ind, 2* sizeof(int));
if (fork() ==0)
{
int t =0;
int ind2[2];
read(fds[x][0], &ind2, 2*sizeof(int));
for( k = ind2[0]; k<ind2[1]; k++)
{
t += numb[k];
}
write(fds[f][1], &t, sizeof(int));
exit(0);
}
}
int m, tmp, total;
total = 0;
for( m = 0; m < f; m++)
{
for( m = 0; m < f; m++)
{
read(fds[f][0], &tmp, sizeof(int));
sleep(5);
total += tmp;
}
printf("DOne calc \n");
printf("Total: %i \n", total);
}
finish = time(NULL);
float runtime = (float)((finish-start)/RUNS);
printf("runtime: %f \n", runtime);
fclose(fp);
return 0;
}

Answer 1

You get random result for the same input because the calculation based on uninitialized int numb[count]; values.
According to the C99 standard, section 6.7.8.10:
If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate.
Because of it int numb[count]; contains some random junk from memory. To get predictive results use explicit initialization:
#include <string.h> // memset
int numb[count];
memset (numb, 0, sizeof(numb)); // Zero-fills
Use the code bellow to put numbers from filename file into numb:
int i = 0;
char line[1024];
fseek(fp, 0, SEEK_SET);
while(fgets(line, sizeof(line), fp) )
{
if( sscanf(line, "%d", &numb[i]) == 1 ) // One number per line
{
++i;
}
}