#include <stdio.h>

#include <stdlib.h>

int main(void){

    int n, m, r, *a;

    printf("Initial size n: ");

    if(scanf("%d", &n)!=1 || n<0){ printf("Invalid n.\n"); return 0; }

    a = (int*)malloc(sizeof(int) * (n>0?n:1));

    if(!a){ printf("Allocation failed.\n"); return 0; }

    printf("Enter %d integers: ", n);

    for(int i=0;i<n;++i) scanf("%d", &a[i]);

    printf("Grow by m elements: ");

    if(scanf("%d", &m)!=1 || m<0){ printf("Invalid m.\n"); free(a); return 0; }

    a = (int*)realloc(a, sizeof(int)*(n+m));

    if(!a){ printf("Realloc failed.\n"); return 0; }

    printf("Enter %d more integers: ", m);

    for(int i=0;i<m;++i) scanf("%d", &a[n+i]);

    n += m;

    printf("Shrink by r elements (<=current size): ");

    if(scanf("%d", &r)!=1 || r<0 || r>n){ printf("Invalid r.\n"); free(a); return 0; }

    n -= r;

    a = (int*)realloc(a, sizeof(int)* (n>0?n:1));

    if(!a){ printf("Realloc failed after shrink.\n"); return 0; }

    printf("Array now (%d elems): ", n);

    for(int i=0;i<n;++i) printf("%d ", a[i]);

    printf("\n");

    free(a);

    return 0;

}