Static stack operations in C - c

Question

i'm trying to perform all operations(push, pop, peep, update, show) on stack using array in C.It's working fine when i am calling the show() at last after calling all of the functions that i need. But whenever i call show() before any of the operations than it is not giving me the appropiate result.
I'm using following code:
int main()
{
push(1);
push(2);
push(3);
push(4);
push(6);
pop();
push(5);
show();//line 8
//push(7);//line 9
//pop();
//peep();
//update();
//show();//line 13
return;
}
void push(int num){//insert an item
if(top==MAXSIZE-1)
{
printf("Overflow condition");
return;
}
top++;
stack[top]=num;
//return;
}
void pop()//delete a item from top
{
int num;
if(top==-1)
{
printf("Underflow condition");
return;
}
num=stack[top];
top--;
//return;
}
void show()//display elements
{
if(top==-1){
printf("Underflow");
return;
}
while(top!=-1){
printf("%d\n",stack[top--]);
}
//return;
}
void peep()//extract information
{
int loc,num;
printf("enter location:\n");
scanf("%d",&loc);
if(top-loc+1 < 0)
{
printf("No item at the given location\n");
return;
}
else{
num=stack[top-loc+1];
printf("\nItem at location %d is %d",loc,num);
}
}
void update(){//update information
int loc,item;
printf("enter new item:");
scanf("%d",&item);
printf("enter location:");
scanf("%d",&loc);
if(top-loc+1 < 0)
{
printf("No item at the given location\n");
return;
}
else{
stack[top-loc+1]=item;
printf("\nItem inserted");
}
}
Here after calling show(),top will point to -1(empty) at line 8,so after that following consequences will be:
push() will insert at position 1 instead of at top.
pop() will show underflow condition.
peep() and update will go in if condition.
So how can i set top to the top element in the stack after once calling the show()?
Thanks.

Answer 1

Your show() method modifies the top pointer and this is wrong:
void show()//display elements
{
if(top==-1){
printf("Underflow");
return;
}
while(top!=-1){
printf("%d\n",stack[top--]); // <--- here 'top--' will modify the top pointer
}
//return;
}
You can change the show() method like this:
void show()//display elements
{
if(top==-1){
printf("Underflow");
return;
}
int i = top; // introducing a new variable to iterate through the stack
while(i!=-1){
printf("%d\n",stack[i--]); // now 'i' is modified
}
//return;
}

Answer 2

One problem with your show function is that, it is also trying to pop out all the data. You should not be doing the top-- in your show function.

Answer 3

//WAP to perform Stack Operation usin C--
1. Push, 2.pop, 3.peep, 4.change, 5.top-of-stack, 6.is-empty, 7.is-full, 8.display
#include<stdlib.h>
#include<stdio.h>
#define max_size 5
int stack[max_size],top=-1,i,x;
/*------ Function Prototype------------*/
void push();
void pop();
void peep();
void display();
void top_stack();
void change();
void is_empty();
/*-------------------------------------*/
int main()
{
int choice;
do{
printf("\n\n--------STACK OPERATIONS-----------\n");
printf("1.Push\n");
printf("2.Pop\n");
printf("3.Peep\n");
printf("4.Display\n");
printf("5.Change\n");
printf("6.TOP\n");
printf("7.exit\n");
printf("-----------------------");
printf("\nEnter your choice:\t");
scanf("%d",&choice);
switch(choice)
{
case 1: push();
break;
case 2: pop();
break;
case 3: peep();
break;
case 4: display();
break;
case 5: change();
break;
case 6: top_stack();
break;
case 7: exit(0);
break;
default: printf("\nInvalid choice:\n");
break;
}
}while(choice!=7);
return 0;
}
void push() //Inserting element in to the stack
{
int item;
if(top==(max_size-1))
{
printf("\nStack Overflow:");
}
else
{
printf("Enter the element to be inserted:\t");
scanf("%d",&item);
top=top+1;
stack[top]=item;
}
}
void pop() //deleting an element from the stack
{
int item;
if(top==-1)
{
printf("Stack Underflow:");
}
else
{
item=stack[top];
top=top-1;
printf("\nThe poped element: %d\t",item);
}
}
void peep()
{
printf("enter the i th element");
scanf("%d",&i);
if(top-i+1<0)
{
printf("\nStack is empty:");
}
else
{
printf("The topmost element of the stack is %d",stack[top-i+1]);
}
}
void display()
{
int i;
if(top==-1)
{
printf("\nStack is Empty:");
}
else
{
printf("\nThe stack elements are:\n" );
for(i=top;i>=0;i--)
{
printf("%d\n",stack[i]);
}
}
}
void change()
{
printf("enter the i th element");
scanf("%d",&i);
if(top-i+1<0)
{
printf("\nStack is empty:");
}
else
{
printf("enter the element to be changed\n");
scanf("%d",&x);
stack[top-i+1]=x ;
printf("The topmost element of the stack is %d",stack[top-i+1]);
}
}
void top_stack()
{
int t;
t=stack[top];
printf("The Topmost element of stack is =%d",t);
}