#include <stdio.h>
#include <string.h>
#include <ctype.h>

#define MAX 20

typedef struct Stack {
    int top;
    int item[MAX];
} Stack;

Stack stack = {-1, {}};

int isEmpty();
int isFull();
int peek();
void push(int value);
int pop();

int precedence(char symbol);
void convertToPostfix(char expression[], char postfix[]);
int evaluate(char postfix[]);

void main() {
    char expression[MAX];
    char postfix[MAX];

    printf("\nMasukkan ekspresi: ");
    gets(expression);
    fflush(stdin);

    convertToPostfix(expression, postfix);

    printf("--------------------------\n");
    printf("\033[34mekspresi\033[m: %s\n", expression);
    printf("\033[33mpostfix\033[m\t: %s\n", postfix);
    printf("\033[32mhasil\t\033[m: %d\n", evaluate(postfix));
    printf("--------------------------\n");
}

// stack operation

int isFull() {
    return stack.top == MAX;
};

int isEmpty() {
    return stack.top == -1;
};

int peek() {
    if (!isEmpty())
        return stack.item[stack.top];
}

void push(int value) {
    if (!isFull()) {
        stack.top += 1;
        stack.item[stack.top] = value;
    }
}

int pop() {
    if (!isEmpty()) {
        int item = peek();
        stack.top -= 1;

        return item;
    }
}

// * etc operation

int precedence(char symbol) {
    switch (symbol) {
        case '+':
        case '-':
            return 1;
        case '/':
        case '*':
            return 2;
        default:
            return 0;
    }
}

void convertToPostfix(char expression[], char postfix[]) {
    int i, ii = 0;

    for (i = 0; i < strlen(expression); i++) {
        char symbol = expression[i];
 
        if (isdigit(symbol)) {
            postfix[ii++] = symbol;
        } else if (symbol == '(') {
            push(symbol);
        } else if (symbol == ')') {
            while (peek() != '(')
                postfix[ii++] = pop();

            pop();
        } else {
            if (precedence(symbol) > precedence(peek())) {
                push(symbol);
            } else {
                while (precedence(symbol) <= precedence(peek()))
                    postfix[ii++] = pop();

                push(symbol);
            }
        }
    }

    while (!isEmpty())
        postfix[ii++] = pop();

    postfix[ii] = '\0';
}

int evaluate(char postfix[]) {
    for (int i = 0; postfix[i] != '\0'; i++) {
        char symbol = postfix[i];
        
        if (isdigit(symbol)) {
            push(symbol - '0');
        } else {
            int number1 = pop();
            int number2 = pop();
            int result = 0;

            switch (symbol) {
                case '+':
                    result = number2 + number1;
                    break;
                case '-':
                    result = number2 - number1;
                    break;
                case '*':
                    result = number2 * number1;
                    break;
                case '/':
                    result = number2 / number1;
                    break;
            }

            push(result);
        }
    }

    return pop();
}