pthread interval template

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>

typedef struct {
    int a, b;
} ThArg;

int a, b, n;

void *troutine(void *arg) {
    ThArg *thArg = (ThArg*)arg;
    printf("Processed [%d %d]\n", thArg->a, thArg->b);
    return NULL;
}

void *zalloc(int nmemb, int sz) {
    void *p = calloc(nmemb, sz);
    if (!p) {
        perror("");
        exit(1);
    }
    return p;
}

int main(void) {
    scanf("%d%d%d", &a, &b, &n);

    int numsPerTh = (b - a + 1) / n;
    pthread_t *threads = (pthread_t*)zalloc(n, sizeof(pthread_t));
    ThArg *thArgs = (ThArg*)zalloc(n, sizeof(ThArg));

    for (int r, i = 0; i < n; i++) {
        thArgs[i].a = a + i * numsPerTh;
        thArgs[i].b = (i == n - 1) ? b : thArgs[i].a + numsPerTh - 1;
        if ((r = pthread_create(&threads[i], NULL, troutine, &thArgs[i]))) {
            fprintf(stderr, "pthread_create error: %s", strerror(r));
            exit(-1);
        }
    }

    for (int r, i = 0; i < n; i++) {
        if ((r = pthread_join(threads[i], NULL))) {
            fprintf(stderr, "pthread_join error: %s", strerror(r));
            exit(-1);
        }
    }

    free(thArgs);
    free(threads);

    return 0;
}