17_stacktop_stackbottom.c

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

struct Stack
{
    int size;
    int top;
    int *arr;
};
int isFull(struct Stack *ptr)
{
    if (ptr->top == (ptr->size - 1))
    {
        return 1;
    }
    return 0;
}
void push(struct Stack *ptr, int value)
{
    if (isFull(ptr))
    {
        printf("Stack Overflow! Cannot push %d to the stack\n", value);
    }
    else
    {
        ptr->top++;
        ptr->arr[ptr->top] = value;
    }
}
int stacktop(struct Stack *ptr)
{
    return ptr->arr[ptr->top];
}
int stackbottom(struct Stack *ptr)
{
    return ptr->arr[0];
}
int peek(struct Stack *ptr, int i)
{
    int arrayIndex = ptr->top - i + 1;
    if (arrayIndex < 0) //to check if this peeking position is not at an index of the array that doesn't exists i.e. index below 0
    {
        printf("Not a valid position for the stack\n");
        return -1;
    }
    else
    {
        return ptr->arr[arrayIndex];
    }
}

int main()
{
    struct Stack *s = (struct Stack *)malloc(sizeof(struct Stack));
    s->size = 10;
    s->top = -1;
    s->arr = (int *)malloc(s->size * sizeof(int));

    push(s, 56);
    push(s, 566);
    push(s, 57);
    push(s, 58);
    push(s, 59);
    push(s, 22);
    push(s, 42);
    push(s, 63);
    push(s, 45);
    push(s, 89);
    for (int i = 1; i <= s->top + 1; i++)
    {
        printf("the value at | peeking position %d | or | index %d of the array | is %d\n", i, (10 - i), peek(s, i));
    }
    printf("The topmost element is %d\n", stacktop(s));
    printf("The bottom element is %d", stackbottom(s));
    return 0;
}

//SO IN STACK ARRAY WE LEARNT following FUNCTIONS : struct STACK, traversal, isEmpty, isFull, push, pop, peek, stacktop, stackbottom