What is wrong with my program implementing a stack in C - c

Question

Hi i have a problem with my stack data structure program. It seems that when i define the size of my array/the imaginary size of array just to call it through a loop the size i defined or specified by the user is being depleted or somewhat edited when i enter a data or push.
For ex. i entered 5 for the size and choose push and then add 2. It is working properly. But if i choose to push data again, it is now passing to the size variable. I do not know understand what is happening...
#include <stdio.h>
#include <ctype.h>
#include <conio.h>
#include <string.h>
#include <stdlib.h>
#define p printf
#define s scanf
int top;
int ar[1];
int size;
main()
{
void push();
int opt, num;
char cont[] = { 'y' };
clrscr();
p("Stacking Program");
p("\n\nData Size: ");
s("%d", &size);
p("\n");
while((cont[0] == 'y') || (cont[0] == 'Y'))
{
clrscr();
p("Stacking Program");
p("\n\nData Size: %d\n\n", size);
p("MAIN MENU\n1. Pop\n2. Push\n3. Pick\n4. View\nChoose: ");
s("%d", &opt);
p("\n");
switch(opt) {
case 1:
pop();
break;
case 2:
if(top > size)
{
p("You can't push more data");
}
else
{
p("Enter data for Data[%d]: ", top);
s("%d", &num);
push(num);
}
break;
case 3:
pick();
break;
case 4:
view();
break;
default:
p("Your choice is not in the list.");
break;
}
p("\n\nDo you want continue\(Y\/N\)?");
s("%s", &cont[0]);
}
}
pop()
{
int a;
if(top < 0)
{
p("Stack empty.");
return 0;
}
else
{
a = ar[top];
p("\(Data[%d] = %d\) removed.", top, a);
top--;
}
}
void push(int b)
{
top++;
ar[top] = b;
}
pick()
{
if(top < 0)
{
p("Nothing to display.");
return 0;
}
else
{
p("\(Data[%d] = %d\) is the last data.", top, ar[top]);
}
}
view()
{
int i;
if(top < 0)
{
p("Nothing to display.");
return 0;
}
else
{
for(i = 1; i < (top + 1); i++)
{
p("Data[%d] = %d\n", i, ar[i]);
}
}
}

Answer 1

You need to define the size of the array at runtime, using the size entered by the user.
instead of:
int top;
int ar[1];
int size;
...
int top = -1;
int *ar = NULL;
int size = 0;
and then after getting size from the user:
if ( size > 0 )
{
ar = malloc(size * sizeof(int));
if ( ar == NULL )
{
printf("ERROR: malloc() failed\n");
exit(2);
}
}
else
{
printf("ERROR: size should be positive integer\n");
exit(1);
}
....
p("\n\nDo you want continue(Y/N)?");
s("%s", &cont[0]);
}
free(ar);
} // end of main
I think the for loop in view() should be:
for(i = 0 ; i <= top ; i++)
also
case 2:
if ( top == ( size - 1 ))

Answer 2

If you don't want to dynamically size the array, another approach is to allocate an array with MAXSIZE elements, where MAXSIZE is "big enough". Also, some other comments:
You declared at the top of your program a character array of size 1:
char cont[] = { 'y' };
But in your scanf line later you try to use this:
s("%s", &cont[0]);
This will overflow your buffer even if the user types just one character, because %s assumes that the buffer has at least two bytes available, one for the character and one for the '\0'. Possible fix:
char cont[] = { 'y', '\0' };
// ...
s("%1s", cont);
Note that cont is the same and more common way of saying &cont[0].
Another problem is with things that might be caught by the compiler if warnings are turned on: all functions should be prototyped before they are mentioned, functions without explicit return type should be declared with type int, and you should not let a function drop off without returning a value even though you declared it to explicitly or implicitly. Also, '(' and ')' do not need to be escaped in string literals.
Here is a modified version with changes noted. I have redefined clrscr() because I don't have conio.h on this system:
#include <stdio.h>
#include <ctype.h>
// #include <conio.h>
#define clrscr() printf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n")
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#define p printf
#define s scanf
#define MAXSIZE 500
// prototypes [Changed]
int pop();
void push(int b);
int pick();
int view();
int top;
int ar[MAXSIZE];
int size;
int main()
{
int opt, num;
char cont[] = { 'y', '\0' }; // [Changed]
clrscr();
p("Stacking Program\n\n");
// keep asking until we get a valid size [Changed]
for (;;)
{
p("Data Size: ");
s("%d", &size);
if (size > 0 && size < MAXSIZE)
break;
printf("Not a valid size!\n");
}
p("\n");
while((cont[0] == 'y') || (cont[0] == 'Y'))
{
clrscr();
p("Stacking Program");
p("\n\nData Size: %d\n\n", size);
p("MAIN MENU\n1. Pop\n2. Push\n3. Pick\n4. View\nChoose: ");
s("%d", &opt);
p("\n");
switch(opt) {
case 1:
pop();
break;
case 2:
if(top > size)
{
p("You can't push more data");
}
else
{
p("Enter data for Data[%d]: ", top);
s("%d", &num);
push(num);
}
break;
case 3:
pick();
break;
case 4:
view();
break;
default:
p("Your choice is not in the list.");
break;
}
p("\n\nDo you want continue(Y/N)?");
s("%1s", cont); // [Changed]
}
return 0;
}
int pop()
{
int a;
if(top == 0) // [Changed]
{
p("Stack empty.");
return 0;
}
else
{
top--; // [Changed]
a = ar[top];
p("(Data[%d] = %d) removed.", top, a);
return a; // [Changed]
}
}
void push(int b)
{
ar[top] = b;
top++; // [Changed]
}
int pick()
{
if(top == 0) // [Changed]
{
p("Nothing to display.");
return 0;
}
else
{
p("(Data[%d] = %d) is the last data.", top, ar[top-1]); // [Changed]
return -1; // [Changed]
}
}
int view()
{
int i;
if(top < 0)
{
p("Nothing to display.");
return 0;
}
else
{
for(i = 0; i < top; i++) // [Changed]
{
p("Data[%d] = %d\n", i, ar[i]);
}
return -1; // [Changed]
}
}