Reverse polish notation in C

here is the starter code : 

/* 
 * File:   main.c
 * Author: MSU
 *
 * Created on March 13, 2019, 1:45 PM
 */

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

#define MAXSIZEI 8
#define MAXSIZEC 7
int top = -1;

int isempty(int stack[]);
int isfull(int stack[]);
int peek(int stack[]);
int pop(int stack[]);
int push(int data, int stack[]);
int printStack(int stack[]);
int size();

int main()
{
    //push item on to the stack
    int stack[8];
    int ssize;
    push(3, stack);
    push(5, stack);
    push(9, stack);
    ssize = size();
    printf(“The size of the stack is: %d\n”, ssize);
    push(1, stack);
    push(12, stack);
    push(15, stack);
    ssize = size();
    printf(“The size of the stack is: %d\n”, ssize);
    
    printf(“Element at top of the stack: %d\n”, peek(stack));
    printStack(stack);
    
    if(isfull(stack) ==1)
        printf(“Stack full\n”);
    else if(isempty(stack)== 1)
        printf(“Stack empty\n”);
    
return 0;    
    
}
int printStack(int stack[])
{
    printf(“Element: \n”);
    while(!isempty(stack)){
        int data = pop(stack);
        printf(“%d\n”, data);
    }
}

int isempty(int stack[])
{
    if(top == -1)
        return 1;
    else 
        return 0;
}

int isfull(int stack[])
{
    if(top == MAXSIZEI)
        return 1;
    else
        return 0;
}

int peek(int stack[])
{
    return stack[top];
}

int pop(int stack[])
{
    int data;
    
    if(!isempty(stack)){
        data = stack[top];
        top = top – 1;
        return data;
    } else{
        printf(“Could not retrieve data, Stack is empty”);
        
    }
}

int push(int data, int stack[]){
    
    if(!isfull(stack)){
        top = top + 1;
        stack[top] = data;
    } else{
        printf(“Count not insert data. Stack is full.\n”);
    }
}
int size()
{
    return top + 1;
}