#include<stdio.h>
#define MAX 40
typedef enum { lparen, rparen, plus, minus, times, divide, mod, eos, operand }
precedence;
char EXPR[MAX];
int stack[20];
int top = -1;
precedence get_token(char *symbol, int *n) {
*symbol = EXPR[(*n)++];
switch (*symbol) {
case '(': return lparen;
case ')': return rparen;
case '+': return plus;
case '-': return minus;
case '*': return times;
case '/': return divide;
case '%': return mod;
case '\0': return eos;
default: return operand;
}
}
void push(int num) {
stack[++top] = num;
}
int pop() {
return stack[top--];
}
int eval() {
precedence token;
char symbol;
int op1, op2, n = 0;
token = get_token(&symbol, &n);
while (token != eos) {
if (token == operand)
push(symbol - '0');
else {
op2 = pop();
op1 = pop();
switch (token) {
case plus:
push(op1 + op2);
break;
case minus:
push(op1 - op2);
break;
case times:
push(op1 * op2);
break;
case divide:
if (op2 == 0) {
printf("Error: Division by zero\n");
return -1;
}
push(op1 / op2);
break;
case mod:
if (op2 == 0) {
printf("Error: Modulo by zero\n");
return -1;
}
push(op1 % op2);
break;
}
}
token = get_token(&symbol, &n);
}
return pop();
}
int main() {
int res;
printf("\nEnter the postfix expression\n");
scanf("%s", EXPR);
res = eval();
if (res != -1)
printf("\nAfter evaluation:\t%d\n", res);
return 0;
}