Problems with threading in C

Question

I'm trying to make a program that takes a text from a file, and after that, it tells me if that text contains a string that I want tho search. The idea is that I must do everything with a process and multiple threads. The number of threads it's a variable number (I should tell from the terminal how many threads I want). If for example, I want 4 threads, the text from the file will be split into 4 strings, and every thread will work with their own string and will search in that string what word I want to find.

For verifying myself that everything works ok, I tried to print some variables on the screen (in server.c). And here I encountered a problem and I can't figure it out. Even if I told the program to print on the screen the "init" variable, it doesn't print anything. Size is printed, nr_thr is printed, everything it's ok until I reach the part when I say to print "init". And obvious, the entire program it's not working.

How can I fix it? It's ok the idea of the program?

This is server.c

###########Server.c##########
#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <pthread.h>

struct argum{
  char string[100];
  char cautat[100];
};


void *cautare(void *data){
  int rez;
  printf("AM ajuns in thread");
  struct argum *argum = data;
  int i,j,k;
  if (strstr(argum->string,argum->cautat)){
    printf("Exista in string");
    rez=1;
  }
  else{
    printf("Nu exista in string asa ceva");
    rez=0;
  }

  return (void*)rez;
}

int main(int argc, char**argv){
  struct argum *argum = malloc(sizeof(struct argum));
  char buffer[1000];
  int nr_thr;
  int df1;
  ssize_t in, out;
  int init=0;
  int i;
  char *a[100];
  char b[1000];

  nr_thr=atoi(argv[3]);
  printf("\n Nr threaduri:%d \n",nr_thr);
  df1 = open(argv[1], O_RDWR);

  if (df1 == -1){
      perror("eroare deschidere ");
      //exit(1);
  }

  int size=lseek(df1, 0, SEEK_END);
  printf("\nSize:%d\n",size);

  lseek(df1, 0, SEEK_SET);

  for(i=0; i<=size; i++){
    if((lseek(df1, i, SEEK_SET))==-1){
      perror("Eroare in fisier");
    }

    in=read(df1,&buffer[i],1);
  }

  printf("In fisier este textul:");
  puts(buffer);

  init = size/nr_thr;

  printf("\nInitial: %d ",init);

  int k=0;
  int l=0;
  int j;

  while(init<=size){
    for(i=init; i<=size/nr_thr; i++){
      b[k]=buffer[i];
      k++;
    }
      a[l]=b;
      init=size/nr_thr;
      if(nr_thr>0){
        nr_thr--;
        l++;
      }
      k=0;
    }


  int rezultat;

  int *return_vals = malloc(nr_thr * sizeof(int));

  pthread_t threads[10];

  for(i=0; i<nr_thr; ++i){
    puts(a[i]);
    argum->string[100]= *a[i];
    argum->cautat[100]= *argv[2];
    pthread_create(&threads[i],NULL,cautare,argum);
  }

  for(i=0; i<nr_thr; ++i){
    rezultat=pthread_join(threads[i],(void**) &return_vals[i]);
    }

  for(i = 0; i < nr_thr; i++)
  printf("Thread %d returned: %d\n", i, return_vals[i]);

  exit(1);
}

This is client.c, where I'm calling everything.

#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <sys/wait.h>
#include <stdlib.h>

int main(){
  int id,d, stare;
  int nr_thr;
  char nume_fis[100], nume_cuv[100];
  char thr[100];
  d=1;
  while(d==1){
    printf("> ");
    scanf("%s %s %d",nume_fis,nume_cuv,&nr_thr);

    sprintf(thr,"%d",nr_thr);
    id=fork();

    if(id<0){
      perror("Eroare la creare proces");
      return -1;
    }
    else if(id==0){ //fiu
      execl("./server","server",nume_fis,nume_cuv,thr,NULL);
      perror("eroare la exec");
    }
    else{
      wait(&stare);
      if(WIFEXITED(stare)){
        printf("%d",WEXITSTATUS(stare));
      }
    }

    printf("\nContinuati?(1 pt da)");
    scanf("%d",&d);
  }
  return 0;
}