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Implementation of Stack to store different data types


Here we will see how to implement stack using structure and union to store different datatypes in stack. First we define the basic structure for elements/items to be stored in the stack. 

struct Items{
 int ele_type;
 union {
  int ivalue;
  float fvalue;
  char *strvalue;
 } stack_element;
};
In the above code, we have defined a Items structure to store the info about the type of items in ele_type variable and a union variable named stack_element to store the actual value of stack items. In union the, ivalue is used to store the integer value, fvalue to store floating value and strvalue to store the string value. If you wish to add other datatype, you can add any datatype within the union. Now we will define the structure to implement the stack. The code below: 

struct Stack{
 int top;
 struct Items element[MAX];
};
In the above code, struct Stack is defined to hold the top of stack and the array of Items structure named element to hold the actual Items defined above. MAX is the stack maximum size. In addition to above two structure we use enum to define the datatypes to be stored in the stack. The code below: 

enum {
 INT, FLOAT, STRING
};
In the above enum the INT have value 0, FLOAT have value 1 and STRING have value 2. If we add other datatypes in the stack_element union, there corresponding datatype value must be added to the enum above.

 Push Operation:

The code below show the push operation on stack defined above: 

void push(struct Stack *s, struct Items *item){
 if(s->top == MAX-1){
  printf("Stack Overflow\n");
 }
 else{
  s->element[++s->top] = *item;
 }
}
 

 Pop Operation:

The code below show the pop operation on stack defined above: 

struct Items pop(struct Stack *s){
 if(s->top == -1){
  printf("Stack Underflow\n");
 }
 else{
  return s->element[s->top--];
 }
}
 

 Displaying the stack elements:

The code below is to display the elements of stack defined above: 

void display(struct Stack *s){
 printf("The Stack items are:\n");
 for(int i = 0; i <= s->top; i++){
  printf("The index %d has type = ", i);
  switch(s->element[i].ele_type){
   case INT : printf("INT and value = %d\n", s->element[i].stack_element.ivalue);
     break;
   case FLOAT : printf("FLOAT and value = %f\n", s->element[i].stack_element.fvalue);
     break;
   case STRING : printf("STRING and value = %s\n", s->element[i].stack_element.strvalue);
     break;
   default : printf("Invalid data type\n");
  }
 }
 printf("\n");
}
 

 The main function:

Now we will see the how to call the push, pop and display functions in the main function: 

int main(){
 struct Stack s;
 s.top = -1;
 
 struct Items i1;
 i1.ele_type = INT;
 i1.stack_element.ivalue = 2;
 push(&s, &i1);
 display(&s);
 pop(&s);
 return 0;
}
 

Program to implement stack to store different data types:

Here is the complete program to for the implementation: 

#include <stdio.h>
#define MAX 10

enum {
 INT, FLOAT, STRING
};

struct Items{
 int ele_type;
 union {
  int ivalue;
  float fvalue;
  char *strvalue;
 } stack_element;
};

struct Stack{
 int top;
 struct Items element[MAX];
};

void display(struct Stack*);
void push(struct Stack *, struct Items *);
struct Items pop(struct Stack*);
int main(){
 struct Stack s;
 s.top = -1;
 
 struct Items i1;
 i1.ele_type = INT;
 i1.stack_element.ivalue = 2;
 
 struct Items i2;
 i2.ele_type = FLOAT;
 i2.stack_element.fvalue = 2.25f;
 
 struct Items i3;
 i3.ele_type = STRING;
 i3.stack_element.strvalue = "Hello World";
 
 push(&s, &i1);
 push(&s, &i2);
 push(&s, &i3);
 
 display(&s);
 
 pop(&s);
 display(&s);
 
 return 0;
}

void push(struct Stack *s, struct Items *item){
 if(s->top == MAX-1){
  printf("Stack Overflow\n");
 }
 else{
  s->element[++s->top] = *item;
 }
}

struct Items pop(struct Stack *s){
 if(s->top == -1){
  printf("Stack Underflow\n");
 }
 else{
  return s->element[s->top--];
 }
}

void display(struct Stack *s){
 printf("The Stack items are:\n");
 for(int i = 0; i <= s->top; i++){
  printf("The index %d has type = ", i);
  switch(s->element[i].ele_type){
   case INT : printf("INT and value = %d\n", s->element[i].stack_element.ivalue);
     break;
   case FLOAT : printf("FLOAT and value = %f\n", s->element[i].stack_element.fvalue);
     break;
   case STRING : printf("STRING and value = %s\n", s->element[i].stack_element.strvalue);
     break;
   default : printf("Invalid data type\n");
  }
 }
 printf("\n");
}
Output: 
The Stack items are:
The index 0 has type = INT and value = 2
The index 1 has type = FLOAT and value = 2.250000
The index 2 has type = STRING and value = Hello World

The Stack items are:
The index 0 has type = INT and value = 2
The index 1 has type = FLOAT and value = 2.250000
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