#include <stdio.h>
#include <stdlib.h>
#define MAX 20
typedef enum { lparen, rparen, plus, minus, times, divide, mod, eos, operand }
precedence;
precedence stack[30];
int top = -1;
char EXPR[MAX];
int isp[] = { 0, 19, 12, 12, 13, 13, 13, 0 };
int icp[] = { 20, 19, 12, 12, 13, 13, 13, 0 };
void push(precedence token);
precedence pop();
precedence get_token(char *symbol, int *n);
void print_token(precedence token);
void postfix();
int main() {
printf("\nEnter the infix expression\n");
if (scanf("%s", EXPR) != 1) {
printf("Error reading input.\n");
return 1;
}
postfix();
return 0;
}
void push(precedence token) {
if (top >= 29) {
printf("Stack Overflow\n");
exit(EXIT_FAILURE);
}
stack[++top] = token;
}
precedence pop() {
if (top == -1) {
printf("Stack Underflow\n");
exit(EXIT_FAILURE);
}
return stack[top--];
}
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 print_token(precedence token) {
switch (token) {
case plus: printf("+"); break;
case minus: printf("-"); break;
case times: printf("*"); break;
case divide: printf("/"); break;
case mod: printf("%%"); break;
}
}
void postfix() {
char symbol;
precedence token;
int n = 0;
top = 0;
stack[0] = eos;
for (token = get_token(&symbol, &n); token != eos; token =
get_token(&symbol, &n)) {
if (token == operand)
printf("%c", symbol);
else if (token == rparen) {
while (stack[top] != lparen)
print_token(pop());
pop();
}
else {
while (isp[stack[top]] >= icp[token])
print_token(pop());
push(token);
}
}
while ((token = pop()) != eos)
print_token(token);
printf("\n");
}