pointer help

Question

// Stack implementation in C++

#include <stdlib.h>
#include <iostream>

using namespace std;

#define MAX 10
int size = 0;

// Creating a stack
struct stack {
int items[MAX];
int top;
};
typedef struct stack st;

void createEmptyStack(st *s) {
s->top = -1;
}

// Check if the stack is full
int isfull(st *s) {
if (s->top == MAX - 1)
return 1;
else
return 0;
}

// Check if the stack is empty
int isempty(st *s) {
if (s->top == -1)
return 1;
else
return 0;
}

// Add elements into stack
void push(st *s, int newitem) {
if (isfull(s)) {
printf("STACK FULL");
} else {
s->top++;
s->items[s->top] = newitem;
}
size++;
}

// Remove element from stack
void pop(st *s) {
if (isempty(s)) {
printf("\n STACK EMPTY \n");
} else {
printf("Item popped= %d", s->items[s->top]);
s->top--;
}
size--;
cout << endl;
}

// Print elements of stack
void printStack(st *s) {
printf("Stack: ");
for (int i = 0; i < size; i++) {
cout << s->items[i] << " ";
}
cout << endl;
}

// Driver code
int main() {
int ch;
st *s = (st *)malloc(sizeof(st));

createEmptyStack(s);

push(s, 1);
push(s, 2);
push(s, 3);
push(s, 4);

printStack(s);

pop(s);

cout << "\nAfter popping out\n";
printStack(s);
}

plz help me finding out why *s has used in every functions argument !

Answer 1

to pass the variable by reference instead of value: this allow changing the variable content from inside the function (else you just modify a local copy)