Start the attendance counters at zero

calloc takes an element count and the size of one element, then allocates space with all its bytes set to zero. For the int counters here, each starting value is zero. You still need to handle a NULL result and call free when finished. The call order is calloc(number_of_elements, size_of_one_element).

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

int main(void) {
    size_t desks = 2;
    int *visits = calloc(desks, sizeof *visits);
    if (visits == NULL) {
        return 1;
    }
    visits[1] = 3;
    printf("Visits: %d, %d\n", visits[0], visits[1]);
    free(visits);
    return 0;
}

Only visits[1] is changed, so the print shows Visits: 0, 3. Had you used malloc, you would need to initialize visits[0] before reading it.