Postfix evaluation

#include<stdio.h>

#include<stdlib.h>

#include<ctype.h>

#define MAX 100

struct stack {

int arr[MAX];

int top;

};

typedef struct stack Stack;

// Function to initialize the stack

void initialisation(Stack* s) {

s->top = -1;

}

// Function that check whether the stack is full or not

int isFull(Stack* s) {

return s->top == MAX - 1;

}

// Function to check if the stack is empty

int isEmpty(Stack* s) {

return s->top == -1;

}

// push operation

void push(Stack* s, int value) {

if (isFull(s)) {

printf("Stack overflow!\n");

} else {

s->arr[++s->top] = value;

}

}

// pop function

int pop(Stack* s) {

if (isEmpty(s)) {

printf("Stack underflow!\n");

return -1;

} else {

int popped_Value = s->arr[s->top--];

return popped_Value;

}

}

int evaluation_of_postfix(char *expr)

{

int i, op1, op2;

Stack s;

initialisation(&s);

for(i=0; expr[i] != '\0'; i++)

{

if(isdigit(expr[i]))

{

push(&s, expr[i] - '0');

}

else if(expr[i] == '+' || expr[i] == '-' || expr[i] == '*' || expr[i] == '/')

{

op2 = pop(&s);

op1 = pop(&s);

switch(expr[i])

{

case '+':

push(&s, op1 + op2);

break;

case '-':

push(&s, op1 - op2);

break;

case '*':

push(&s, op1 * op2);

break;

case '/':

push(&s, op1 / op2);

break;

}

}

}

return pop(&s);

}

void main()

{

char postfix[MAX];

printf("Enter a postfix expression: ");

scanf("%s", postfix);

int result = evaluation_of_postfix(postfix);

printf("The result of the postfix expression is: %d\n", result);

}