Stack using Array

The goal: a working stack program

This is a hands-on practice program. If you want to first understand what a stack is and how LIFO works, read the stack in C concept lesson. Here we go straight to building a complete, menu-driven stack program using an array that you can compile and run.

What the program will do

The program keeps showing a menu and performs whatever the user picks:

• 1. Push — add a number to the top
• 2. Pop — remove the top number
• 3. Peek — see the top number without removing it
• 4. Display — show all numbers from top to bottom
• 5. Exit

The complete program

#include <stdio.h>
#define SIZE 100
int stack[SIZE];
int top = -1;

void push(int x) {
    if (top == SIZE - 1) { printf("Stack full\n"); return; }
    stack[++top] = x;
    printf("%d pushed\n", x);
}
void pop() {
    if (top == -1) { printf("Stack empty\n"); return; }
    printf("%d popped\n", stack[top--]);
}
void peek() {
    if (top == -1) { printf("Stack empty\n"); return; }
    printf("Top = %d\n", stack[top]);
}
void display() {
    if (top == -1) { printf("Stack empty\n"); return; }
    printf("Stack: ");
    for (int i = top; i >= 0; i--) printf("%d ", stack[i]);
    printf("\n");
}
int main() {
    int choice, value;
    while (1) {
        printf("\n1.Push 2.Pop 3.Peek 4.Display 5.Exit: ");
        scanf("%d", &choice);
        switch (choice) {
            case 1: printf("Value: "); scanf("%d", &value); push(value); break;
            case 2: pop(); break;
            case 3: peek(); break;
            case 4: display(); break;
            case 5: return 0;
            default: printf("Invalid\n");
        }
    }
}

A sample run

Dry run of push and pop

Each push moves top up before storing; each pop reads at top then moves it down. The display loop runs from top down to 0.

Common mistakes

• Starting top at 0 instead of -1 for an empty stack.
• Forgetting the full/empty checks, causing overflow or reading invalid memory.
• Displaying from 0 upward instead of top downward (wrong order).
• Mixing ++top (pre) and top++ (post) incorrectly in push/pop.

Summary

• An array stack uses an array plus a top index starting at -1.
• A menu-driven loop exercises push, pop, peek and display.
• Push moves top up then stores; pop reads then moves down.
• Display runs from top down to 0 to show LIFO order.
• Always guard against full and empty conditions.