c - bad output from pipe with multiple processes -

in following code, have 2 pipes, one, fd[] handles ferrying range variable child processes. other pipe rw[] responsible printing results of method. fd works correctly, rw prints garbage. both range , narc_num long , have sucessfully printed string , char through rw pipe. ideas? thanks.

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <math.h> #include <string.h>  /**  * process propigating version of narcisstic base-10 number generator **/  /**  * narcissistic number number of digits, when raised power n n number of digits in number, equla number itseld.  * examples:  * 2^1 = 2 **/  void isnarcissisticnumber(int rw[], long min, long max){ //    printf("min %ld max %ld\n", min, max);     long n;     for(n = min; n <= max; n++){     long num = n;         int digits = floor(log10(num)) + 1;         int digit_arr[digits];         long narc_num = 0;         int index = 0;         do{             digit_arr[index++] = num%10;             num /= 10;         }while(num > 0);         index = 0;         for(index; index < digits; index++){             narc_num += pow(digit_arr[index], digits);         }         if(narc_num == n){         printf("%ld\n", n);         // parent: writing only, close read-descriptor.         close(rw[0]);         write(rw[1], &n, sizeof(long));                 // close write descriptor                 close(rw[1]);     }     } }  int main(int argc,           // number of strings in array argv           char *argv[]){      // array of command-line argument strings)     //check there 1 passed in parameter in addition program name @ argv[0]       if(argc != 2){         printf("args found: %d. 1 arg required\n", argc);         return;     }     //check argv passed in int     if(!atoi(argv[1])){         printf("argument shoud # of processes proc.\n");         return;     }     int num_processes = atoi(argv[1]);     //counter narcissistic numbers     long offset = 10000;     long range= -offset;      //file pipe     int fd[2];     //printing pipe     int rw[2];     int n = 0;     long output;     while(n < num_processes){ // -1 offset line array index num_processes arg        pipe(rw);     pipe(fd);         pid_t process = fork();     pid_t child_process;         int status;     if(process == 0){ //chid process --> execute program         child_process = process;                 /* duplicate input side of pipe stdin */         // chid: reading only, close write-descriptor             close(fd[1]);         read(fd[0], &range, sizeof(range));         close(fd[0]);         isnarcissisticnumber(rw, range, range+offset-1);     }else if(process != 0){         // parent: writing only, close read-descriptor.             close(fd[0]);         range += offset;         write(fd[1], &range, sizeof(range));         // close write descriptor             close(fd[1]);          // current child process complete routine befire checking output         wait(&child_process);                //read printing pipe         close(rw[1]);         while(read(rw[0], &output, sizeof(long))){             printf("printer %ld\n", output);         }         close(rw[0]);     }else{ //failed fork             printf("process failed fork!\n");             return -1;         }     n++;     } } 

edit #1: while made parent check after child completed, doesn't fix output of pipe, 0 printf shows otherwise.

i'm not sure fix problems have logic issue. in computation routine can write 0 or more longs output. in print (parent) routine, expect 1 value come through. if nothing sent, read fail. if multiple values sent, read first one. first fix check return value read , loop on it.

note - idea wait() on child process.