Stacks and Queues (Basic Data Structures)

This lesson covers implementing a stack and a queue in C, so you understand how to pick the right way to add and remove data for the job. It's for anyone searching "C stack queue implementation."

A stack is "last in, first out," and a queue is "first in, first out." It helps to picture the difference between "a stack of books" and "a line of people."

The example combines an array with an index variable, top, showing how stack[++top] = 'A' pushes a value and stack[top--] pops the last one (a stack), alongside using front/rear indices to build a queue.

A common early mistake is not realizing C has no dedicated type for this — you need to manage it yourself by combining an array with an index. Getting the timing of index updates wrong leads to accessing the wrong value.

In real projects, the ability to implement data structures like this efficiently, within limited memory, matters especially in embedded systems development.

📖 Reference code

#include <stdio.h>

int main(void) {
    char stack[10];
    int top = -1;
    stack[++top] = 'A';
    stack[++top] = 'B';
    printf("%c\n", stack[top--]);

    char queue[10];
    int front = 0, rear = 0;
    queue[rear++] = 'A';
    queue[rear++] = 'B';
    printf("%c\n", queue[front++]);
    return 0;
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).