My static stack code is not running properly

Question

#include <stdio.h>
#include <stdlib.h>
#define N 5
int stack[N];
int top = -1;
void push()
{
    int x;
    printf("Enter data");
    scanf("%d", &x);
    if (top == N - 1)
    {
        printf("Overflow");
    }
    else
    {
        top++;
        stack[top] = x;
    }
}

void pop()
{
    int item;
    if (top == -1)
    {
        printf("Underlfow");
    }
    else
    {
        item = stack[top];
        top--;
        printf("%d", item);
    }
}

void peek()
{
    if (top == -1)
    {
        printf("Underflow");
    }
    else
    {
        printf("%d", stack[top]);
    }
}

void display()
{
    int i;
    for (i = top; i >= 0; i--)
    {
        printf("%d\n", stack[top]);
    }
}

int main()
{
    int ch;
    do
    {
        printf("\n1.push\n2.pop\n3.peek\n4.display");
        scanf("%d", &ch);
        switch (ch)
        {
        case 1:
            push();
            break;

        case 2:
            pop();
            break;

        case 3:
            peek();
            break;

        case 4:
            display();
            break;

        case 5:
            exit(0);
            break;

        default:
            printf("invalid key pressed");
            break;
        }
    } while (ch != 0);
    return 0;
}

So it is the code which i wrote following a tutorial on youtube In push function if i excced the array size which is 5 it will still take values instead of printing overflow and when i try to display it, it will display all values same

before i was geting a error at getch(); while using void main() so i change it to int main() and used return 0; it is still not working.

Answer 1

So it is the code which i wrote following a tutorial on youtube In push function if i excced the array size which is 5 it will still take values instead of printing overflow and when i try to display it, it will display all values same

1. Your logic is to always allow you to enter values. But they are not inserted in the stack (and instead "Overflow" is printed). This is because you ask for the value before checking if the stack is full. Just make the test before, and put the scan inside the else part of the if statement.

void push()
{
    int x;

    if (top == N - 1) {
        /* put \n chars at end of lines in output statements
         * like this ---vv      */
        printf("Overflow\n");
    } else {
        printf("Enter data ");
        fflush(stdout);
        scanf("%d", &x);
        top++;
        stack[top] = x;
    }
}

2. The problem of printing always the top of the stack is basically that you print stack[top], instead of stack[i], in the display() function loop. You should use this code instead.

void display()
{
    int i;
    for (i = top; i >= 0; i--)
    {
        /* use i here --------------v */
        printf("%d: %d\n", i, stack[i]);  
    }
}

3. This is not an error, but will save you trouble in the future. Get used to put the \n char at the end of the printing format, instead of at the beginning, if you are going to print a complete line. I understand that you want to avoid it when prompting the user, so you avoid it. But the stdio library uses buffering, so it doesn't print things when you ask it for, so it delays the printing of strings (on an interactive session) until you do printf a '\n' char (if the output device is a terminal), or before reading from stdin (also, if the input device is a terminal). This can make a mess if you print your strings without the trailing '\n'. And more, if you redirect your output, this means using a pipe (so, it is not a terminal). Then, no output is done until the buffer fills completely (meaning over 10kb of data, usually 16kb on modern unix/linux systems) You will see your program doing things while no output has been output, and you won't know why.

4. You don't use getch() in your code, so i think you have posted a different version of the code you are talking about.

My code, after edition, leads to:

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

#define N 5

int stack[N];
int top = -1;

void push()
{
    if (top == N - 1) {
        /* no overflow yet, not if we check beforehand :) */
        printf("Stack full, cannot push()\n");
    } else {
        int x;

        printf("Enter data ");
        fflush(stdout); /* to flush the output (no \n at end) */
        scanf("%d", &x);
        top++;
        stack[top] = x;
        printf("Push: %d to position %d\n", x, top);
    }
}

void pop()
{
    if (top == -1) {
        /* the appropiate message is stack empty, no underflow has
         * occured yet.  We are preventing it */
        printf("Stack empty, cannot pop()\n");
    } else {
        int item = stack[top];
        printf("Pop: %d from pos %d\n", item, top);
        top--;
    }
}

void peek()
{
    if (top == -1) {
        /* no underflow yet, we are preventing it */
        printf("Stack empty, cannot peek()\n");
    } else {
        printf("Peek: %d on pos %d\n", stack[top], top);
    }
}

void display()
{
    int i;
    printf("Stack contents:\n");
    for (i = top; i >= 0; i--) {
        printf("> %d: %d\n", i, stack[i]);
    }
}

int main()
{
    int ch = 5; /* so we exit if no valid input is made in scanf() */

    do {
        printf("1.push\n"
               "2.pop\n"
               "3.peek\n"
               "4.display\n"
               "5.exit\n");
        scanf("%d", &ch);

        switch (ch) {

        case 1:
            push();
            break;

        case 2:
            pop();
            break;

        case 3:
            peek();
            break;

        case 4:
            display();
            break;

        case 5:
            break;

        default:
            printf("Input invalid option\n");
            break;

        }
    } while (ch != 5); /* option 5 is to exit */

    return 0;
}