11.Implement stack using array.

//Program to implement stack using array.
#include<stdio.h>
#include<conio.h>

struct stack {
    int arr[10];
    int top;
} st;

int isFull() {
    if (st.top == 9) {
        return 1;
    }
    else {
          return 0;
    }
}

int isEmpty() {
    if (st.top == -1) {
        return 1;
    }
    else {
        return 0;
    }
}

void push() {
    if (!isFull()) {
        int val;
        printf("Enter value to be pushed: ");
        scanf("%d", &val);

        st.top++;
        st.arr[st.top] = val;

        printf("Successfully pushed %d in the stack.", val);
        getch();
    }
    else {
        printf("The Stack is Full.");
        getch();
    }
}

void pop() {
    if (!isEmpty()) {
        printf("Successfully popped %d from the stack.", st.arr[st.top]);
        st.top--;
        getch();
    }
    else {
        printf("The stack is Empty.");
        getch();
    }
}

void display() {
    int i;

    if (isEmpty()) {
        printf("The stack is Empty.");
        getch();
    }
    else {
        for (i = st.top; i >= 0; i--) {
            printf("%d\n", st.arr[i]);
        }
        getch ();
    }
}

void main()
{
    char choice;

    clrscr();

    st.top = -1;

    while (1) {
        clrscr();

        printf("1.Push\n2.Pop\n3.Display\n4.Exit\n");
        choice = getch();

        switch (choice) {
            case '1':
                push();
                break;

            case '2':
                pop();
                break;

            case '3':
                display();
                break;

            case '4':
                return;

            default:
                printf("Invalid input.");
                getch();
        }
    }
}