creating process with fork in loop - loops

Question

I'm trying to make a program that will print all the prime number between 2 values (lvan (lower value) and uval (upper value)), print some of them by the user choice (nval) and will find them by using number of child processes (pval is the number of children's).
so the problem is that I don't know how to make my program make only the asked amount of child processes and preventing my child process from creating it's own childs.
I will mark the line that I thought that I need to enter the code that will make everything work well (may be a wrong line).
I've tried to kill the child process but that's terminated all the program, I've tried to make the child return a value (with return and exit commands) but that terminated the program as well.
What should I do ?
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/mman.h>
#include <sys/wait.h>
void parseargs(char *argv[], int argc, int *lval, int *uval, int *nval, int *pval);
int isprime(int n);
int countFlags(char* arr, int size);
int main (int argc, char **argv)
{
int lval = 1; //def val
int uval = 100; //def val
int nval = 10; //def val
int pval = 4; //def val
int count = 0;
int rc,num;
// Parse arguments
parseargs(argv, argc, &lval, &uval, &nval, &pval);
if (uval < lval)
{
fprintf(stderr, "Upper bound should not be smaller then lower bound\n");
exit(1);
}
if (lval < 2)
{
lval = 2;
uval = (uval > 1) ? uval : 1;
}
if (pval < 0)
pval=4;
char *flagarr = mmap ( NULL, (uval-lval+1)*sizeof(char),
PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0 );
if (flagarr == MAP_FAILED)
exit(2);
//start forks
for(int i =0; (i<pval); i++){
if(rc=fork()<0)
{
printf("fork failed");
exit(1);
}
if(rc==0)
{
for (num = lval+i; num <= uval; num+=pval)
{
if (isprime(num))
{
flagarr[num - lval] = 1;
count ++;
} else {
flagarr[num - lval] = 0;
}
}
printf("%d\n",i);
//problematic line imo ??
}
}
for(int i =0; (i<pval) ; i++)
wait(NULL);
// Print results
printf("Found %d primes%c\n", count, count ? ':' : '.');
for (num = lval; (num <= uval) && (nval) ; num++)
if (flagarr[num - lval])
{
nval--;
count--;
printf("%d%c", num, (count && nval) ? ',' : '\n');
}
munmap(flagarr,(uval-lval+1));
return 0;
}
// NOTE : use 'man 3 getopt' to learn about getopt(), opterr, optarg and optopt
void parseargs(char *argv[], int argc, int *lval, int *uval, int *nval, int *pval)
{
int ch;
opterr = 0;
while ((ch = getopt (argc, argv, "l:u:n:p:")) != -1)
switch (ch)
{
case 'l': // Lower bound flag
*lval = atoi(optarg);
break;
case 'u': // Upper bound flag
*uval = atoi(optarg);
break;
case 'n':
*nval = atoi(optarg);
break;
case 'p':
*pval = atoi(optarg);
break;
case '?':
if ((optopt == 'l') || (optopt == 'u')|| (optopt == 'n')|| (optopt == 'p'))
fprintf (stderr, "Option -%c requires an argument.\n", optopt);
else if (isprint (optopt))
fprintf (stderr, "Unknown option `-%c'.\n", optopt);
else
fprintf (stderr, "Unknown option character `\\x%x'.\n", optopt);
exit(1);
default:
exit(1);
}
}
int countFlags(char* arr, int size)
{
int ret =0;
for(int i=0;i<size;i++)
ret+=arr[i];
return ret;
}
int isprime(int n)
{
static int *primes = NULL; // NOTE: static !
static int size = 0; // NOTE: static !
static int maxprime; // NOTE: static !
int root;
int i;
// Init primes array (executed on first call)
if (primes == NULL)
{
primes = (int *)malloc(2*sizeof(int));
if (primes == NULL)
exit(1);
size = 2;
primes[0] = 2;
primes[1] = 3;
maxprime = 3;
}
root = (int)(sqrt(n));
// Update primes array, if needed
while (root > maxprime)
for (i = maxprime + 2 ; ; i+=2)
if (isprime(i))
{
size++;
primes = (int *)realloc(primes, size * sizeof(int));
if (primes == NULL)
exit(1);
primes[size-1] = i;
maxprime = i;
break;
}
// Check 'special' cases
if (n <= 0)
return -1;
if (n == 1)
return 0;
// Check prime
for (i = 0 ; ((i < size) && (root >= primes[i])) ; i++)
if ((n % primes[i]) == 0)
return 0;
return 1;
}