a.cpp

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

int main(){
    int *a;
    a = (int *) malloc(sizeof(int) * 12);
    for (int i = 0; i < 12 ; i++)
        a[i] = i;
    for (int i = 0; i < 12 ; i++)
        printf("%i\n", a[i]);

    a = (int *) realloc((void *) a, sizeof(int) * 25);
    for (int i = 12; i < 24 ; i++)
        a[i] = i;
    for (int i = 0; i < 24 ; i++)
        printf("%i\n", a[i]);

    return 0;
}