Handler for SIGCHLD signals

Question

The code doesn't work and it goes in loop. I think the error is in the gestore method, that is a handler for SIGCHLD signals. This is the first time I use a handler to capture SIGCHLD signals. This program continue to casually extracts from 0 to argv[1] until a number appears argv[1] times. If it's not clear you can test my old program that I put at the end of question. Can you help me finding the error?

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

int a;
void gestore(int segnale);
int main(int argc, char * argv[]){
    int n = atoi(argv[1]), i, pid;
    int * vec;
    vec = malloc((n+1)*sizeof(*vec));
    memset (vec, 0, sizeof(*vec));
    char * newargv[] = {argv[0], argv[1] , NULL};
    for(i = 0; i < n; i++){
        pid = fork();
        if (pid == 0)
            execve("./throw-dice", newargv, NULL);
        signal(SIGCHLD, gestore);
        vec[WEXITSTATUS(a)]++;
    }
    while(vec[i] != n){
        for(i = 1; i < n+1 && vec[i] != n; i++){
            if(vec[i] != 0){
                pid = fork();
                if (pid == 0)
                    execve("./throw-dice", newargv, NULL);
                signal(SIGCHLD, gestore);
                vec[WEXITSTATUS(a)]++;
            }
        }
    }
    printf("The value %d is appeared %d times!\n", i, vec[i]);
    while (wait(&a) != -1);
    free(vec);
}

void gestore(int segnale){
    signal(segnale, SIG_IGN);
    waitpid(WAIT_ANY, &a, WNOHANG);
    signal(segnale, gestore);
}

My goal was to modify my old program (that works) changing the way I capture the exit status of childs. From syncronically with "wait" to asyncronically with a gestore method that handle SIGCHLD signals. This is my old program:

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

int main(int argc, char * argv[]){
    int n = atoi(argv[1]), a, i, pid;
    int * vec;
    vec = malloc((n+1)*sizeof(*vec));
    memset (vec, 0, sizeof(*vec));
    char * newargv[] = {argv[0], argv[1] , NULL};
    for(i = 0; i < n; i++){
        pid = fork();
        if (pid == 0)
            execve("./throw-dice", newargv, NULL);
        wait(&a);
        vec[WEXITSTATUS(a)]++;
    }
    while(vec[i] != n){
        for(i = 1; i < n+1 && vec[i] != n; i++){
            if(vec[i] != 0){
                pid = fork();
                if (pid == 0)
                    execve("./throw-dice", newargv, NULL);
                wait(&a);
                vec[WEXITSTATUS(a)]++;
            }
        }
    }
    printf("The value %d is appeared %d times\n", i, vec[i]);
    while (wait(&a) != -1);
    free(vec);
}

//throw-dice.c

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char * argv[]) {
    int n, val;
    // Must have an argument
    if (argc < 2) {
        exit(-1);
    }
    // the 1st argument must be a positive number
    if ((n = atoi(argv[1])) <= 0) {
        exit(-1);
    }
    //  sleep(1); // sleep a bit
    srand(getpid()); // initialize the random seed with PID
    val = rand() % n + 1;
    printf("(PID=%d): got number %d\n", getpid(), val);
    exit(val);
}