Stack Program in C (Concept, Algorithm & C program example)

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Last Updated : 04/01/2023

Posted By :- Vinnu

In this article, we will be implementing C language program to implement stack to perform push, pop & display operation in it. But before we proceed to that we must have knowledge of Stack.

Stack data structure

Stack is a linear data structure which follows a particular order in which the operations are performed. It can be represented by a real physical stack or pile, a structure where insertion and deletion of items take place at one end called top of the stack.

The basic implementation of a stack is also called a LIFO (Last In First Out) to demonstrate the way it accesses data, since as we will see there are various variations of stack implementations.

Common example: Suppose at your home you have multiple chairs then you put them together to form a vertical pile. From that vertical pile the chair which is placed last is always removed first.

Operations performned on stack

Mainly two basic operations(PUSH, POP ) are performed in the stack, here are the list of operations with brief explanation:

Push: Adds an item on the top of the stack. If the stack is full, then it is said to be an Overflow condition.
Pop: Removes an item from the top of the stack. The items are popped in the reversed order in which they are pushed. If the stack is empty, then it is said to be an Underflow condition.
Peek or Top: Returns the top element of the stack.
isEmpty: True if no more items can be popped and there is no top item
is-full: True if no more items can be pushed
get-size: Returns the number of elements on the stack.

Declaration of Stack

typedef struct stack
{
  int data[MAX];
  int top;
}stack;

Algorithm for stack program in C

We will be focusing on two main operations of Stack, i.e, Push, & POP, so I will be creating Algorithm for PUSH, POP & Check if Stack is full or empty

Algorithm for PUSH

Step 1: If TOP >= SIZE – 1 then
               Print "Stack Overflow"
Step 2: Else TOP = TOP + 1
Step 3: STACK [TOP] = X
Step 4: Exit

Algorithm for POP

Step 1: If TOP = -1 then
             Print "Stack is Underflow"
Step 2: Return STACK [TOP]
Step 3: TOP = TOP - 1
Step 4: Exit

Algorithm to check if Stack is FULL

Step 1: IF TOP = MAX then
        STATUS:=true;
Step 2: Otherwise
        STATUS:=false;
Step 3: End of IF
Step 4: Exit

Algorithm to check if Stack is EMPTY

Step 1: IF TOP = 0 then
        STATUS:=true;
Step 2: Otherwise
        STATUS:=false;
Step 3: End of IF
Step 4: Exit

C program to implement Stack PUSP, POP operation

#include<stdio.h>

//Stack size
#define SIZE 5

//Declare stack functions
void push(int *STACK,int x);
void pop(int *a);
void display(int *a);

//Decalre TOP and STACK variables
int TOP=-1;
int STACK[SIZE];

void main()
{
      int x,ch;
      
      //implement continues while loop using 1
      while(1)
      {
          printf("Select Your Choice:\n");
          printf("(1) PUSH\n");
          printf("(2) POP\n");
          printf("(3) Display\n");
          printf("(4) Enter 4 to exit \n");
          printf("Enter Your Choice\n");
          scanf("%d",&ch);
          switch(ch)
          {
              case 1:
                   printf("Enter Element:");
                   scanf("%d",&x);
                   push(STACK,x);
                   break;
              case 2:
                   pop(STACK);
                    break;
              case 3:
                   display(STACK);
                   break;
              case 4:
                   //break loop using exit
                   exit(0);
          }
}
}

void push(int *STACK,int x)
{
     //check if TOP value (TOP=current stack value) is greater than or equal SIZE
      // if yes Stack Overlfowed cannot enter new data in STACK
      if(TOP>=SIZE-1)
      {
         printf(" Stack Overflowed ");
      }
      //if there is more space in STACK eneter data
      else
      {
          TOP=TOP+1;
          STACK[TOP]=x;
      }
}

void pop(int *STACK)
{
      int x;
       //check is TOP (TOP=current stack value) of stack is equal to -1
       //then is it already empty
      if(TOP==-1){
          printf("Stack is Underflow");
      }
      //remove top element from Stack
      else
      {
          printf("Deleted Element is %d\n",STACK[TOP]);
           //decrement TOP value
          TOP=TOP-1;
      }
}

void display(int *STACK)
{
      int i;
      //check is TOP (TOP=current stack value) of stack is equal to -1
       //then is it already empty
      if(TOP==-1){
          printf("Stack is Empty\n");
      }
      else
      {
          printf ("\n Stack element are \n");
          //loop through each value of stack and print it
          for(i=TOP;i>=0;i--)
          {
             printf("%d\t",STACK[i]);
          }
      }
}

I have commented out code for you to understand important lines of the code for you to understand it, here is the output of the code which I ran on online compiler here

Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
1
Enter Element:11
Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
1
Enter Element:22
Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
1
Enter Element:33
Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
1
Enter Element:44
Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
3

 Stack element are 
44	33	22	11	Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
2
Deleted Element is 44
Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
2
Deleted Element is 33
Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
3

Stack element are 
22	11	Select Your Choice:
(1) PUSH
(2) POP
(3) Display
(4) Enter 4 to exit 
Enter Your Choice
4