How I can fix the error in the doublestack function ?

#include <iostream>
using namespace std;
struct Stack {
    int top;
    int capacity;
    int *array;
};
struct Stack *createStack(int capacity){
    struct Stack *S=new struct Stack;
    if(!S)
        return NULL;
    S->capacity=capacity;
    S->top=-1;
    S->array=new int[capacity];
    if (!S->array)
        return NULL;
    return S;
}
int isEmpty(struct Stack *S){
    return(S->top==-1);
}
int size(struct Stack *S){
    return(S->top+1);
}
int isFull(struct Stack *S){
    return(S->top==S->capacity-1);
}
void doubleStack(struct Stack *S){
    S->capacity*=2;
    S->array=realloc(S->array,S->capacity * sizeof(int));
}
void push(struct Stack *S,int data){
    if (isFull(S))
        doubleStack(S);
    else
        S->array[++S->top]=data;
}
int pop(struct Stack *S){
    if (isEmpty(S)){
        cout<<"Stack is Empty"<<endl;
        return INT16_MIN;
    }
    else
        return(S->array[S->top--]);
}
int peek(struct Stack *S){
    if (isEmpty(S)){
        cout<<"Stack is Empty"<<endl;
        return INT16_MIN;
    }
    else
        return(S->array[S->top]);
}
void deleteStack(struct Stack *S){
    if (S){
        if (S->array){
            delete S->array;
            delete S;
        }
    }
}
int main() {
    int capacity=5;
    struct Stack *stack= createStack(capacity);
    for (int i = 0; i < 2*capacity; ++i) {
        push(stack,i);
    }
    cout<<"top:"<<peek(stack)<<endl;
    cout<<"size:"<<size(stack)<<endl;
    for (int i = 0; i < capacity; ++i) {
        cout<<pop(stack)<<" ";
    }
    cout<<endl;
    if (isEmpty(stack))
        cout<<"Stack is Empty"<<endl;
    else
        cout<<"Stack is not Empty"<<endl;
    deleteStack(stack);
    return 0;
}

void doubleStack(struct Stack *S){
    S->capacity*=2;
    S->array=realloc(S->array,S->capacity * sizeof(int));
}