DATA STRUCTURES PROGRAM • STACKS & EXPRESSIONS

Implement Stack Operations Using an Array

Learn how to implement stack operations using an array using a clear C program.

BeginnerStackLIFOpush/pop

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

Top = 30
Popped = 30
New top = 20

COMPLETE C PROGRAM

Complete C implementation

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

#define CAPACITY 50
struct Stack { int values[CAPACITY]; int top; };
void stack_init(struct Stack *stack) { stack->top = -1; }
int stack_empty(const struct Stack *stack) { return stack->top < 0; }
void stack_push(struct Stack *stack, int value)
{
    if (stack->top + 1 >= CAPACITY) { puts("Stack overflow."); exit(EXIT_FAILURE); }
    stack->values[++stack->top] = value;
}
int stack_pop(struct Stack *stack)
{
    if (stack_empty(stack)) { puts("Stack underflow."); exit(EXIT_FAILURE); }
    return stack->values[stack->top--];
}
int stack_peek(const struct Stack *stack)
{
    if (stack_empty(stack)) { puts("Stack is empty."); exit(EXIT_FAILURE); }
    return stack->values[stack->top];
}

int main(void)
{
    struct Stack stack;
    stack_init(&stack);
    stack_push(&stack, 10); stack_push(&stack, 20); stack_push(&stack, 30);
    printf("Top = %d\n", stack_peek(&stack));
    printf("Popped = %d\n", stack_pop(&stack));
    printf("New top = %d\n", stack_peek(&stack));
    return 0;
}

CURRENT STEP

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EXPECTED OUTPUT FOR THE SAMPLE

Top = 30
Popped = 30
New top = 20

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Use a top index to identify the most recently pushed array element.
Display the computed result.

Use a top index to identify the most recently pushed array element.

EFFICIENCY

Time and space complexity

Time complexity

O(1) per operation

Auxiliary space

O(n)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

Check this

Initialize variables before using their values.

Check this

Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.