#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <ctype.h>
#define MAX 100

// === 全域變數宣告 ===
char input[MAX];
char postfix[MAX];
char stack[MAX];
double numStack[MAX];
int top = -1;
int numTop = -1;

// === 函式宣告 ===
int get_priority(char op);
int is_operator(char c);
double calculate(double a, double b, char op);
void convert_to_postfix();
double evaluate_postfix();

// === 檢查運算子優先順序 ===
int get_priority(char c){
    if(c=='+' || c=='-'){
        return 1;
    }else if(c=='*' || c=='/'){
        return 2;
    }else if(c=='^'){
        return 3;
    }else{
        return 0;
    } 
}

// === 檢查字元是否為運算子 ===
int is_operator(char c) {
    return (c == '+' || c == '-' || c == '*' || c == '/' || c == '^');
}

// === 執行運算 ===
double calculate(double a, double b, char op) {
    switch(op) {
        case '+': return a + b;
        case '-': return a - b;
        case '*': return a * b;
        case '/': 
            if(b != 0) return a / b;
            printf("錯誤：除數不能為零！\n");
            exit(1);
        case '^': return pow(a, b);
        default: return 0;
    }
}

// === 轉換為後序表達式 ===
void convert_to_postfix() {
    int i = 0, j;
    int postfix_index = 0;
    top = -1;
    char number_str[MAX];
    int is_negative;
    
    while(input[i] != '\0') {
        if(isdigit(input[i]) || input[i] == '.' || 
           (input[i] == '-' && (i == 0 || input[i-1] == '(' || is_operator(input[i-1])))) {
            // 處理數字（包括負數）
            is_negative = 0;
            int num_len = 0;
            
            // 檢查是否為負數
            if(input[i] == '-') {
                is_negative = 1;
                i++;
            }
            
            // 收集完整數字字串
            while(input[i] != '\0' && (isdigit(input[i]) || input[i] == '.')) {
                number_str[num_len++] = input[i++];
            }
            number_str[num_len] = '\0';
            i--;  // 回退一個位置，因為外層 while 會再加一
			
            // 輸出數字
            printf("%s ", number_str);
            if(is_negative) {
                printf("- ");
            }

            // 將數字加入後序表達式
            for(j = 0; j < num_len; j++) {
                postfix[postfix_index++] = number_str[j];
            }
            postfix[postfix_index++] = ' ';
            if(is_negative) {
                postfix[postfix_index++] = '-';
                postfix[postfix_index++] = ' ';
            }
        }
        else if(input[i] == '(') {
            stack[++top] = input[i];
        }
        else if(input[i] == ')') {
            while(top >= 0 && stack[top] != '(') {
                printf("%c ", stack[top]);
                postfix[postfix_index++] = stack[top];
                postfix[postfix_index++] = ' ';
                top--;
            }
            if(top >= 0) top--;
        }
        else if(is_operator(input[i])) {
            // 如果不是處理負數的減號
            if(!(input[i] == '-' && (i == 0 || input[i-1] == '(' || is_operator(input[i-1])))) {
                while(top >= 0 && stack[top] != '(' && 
                      (get_priority(stack[top]) > get_priority(input[i]) ||
                       (get_priority(stack[top]) == get_priority(input[i]) && input[i] != '^'))) {
                    printf("%c ", stack[top]);
                    postfix[postfix_index++] = stack[top];
                    postfix[postfix_index++] = ' ';
                    top--;
                }
                stack[++top] = input[i];
            }
        }
        i++;
    }
    
    while(top >= 0) {
        printf("%c ", stack[top]);
        postfix[postfix_index++] = stack[top];
        postfix[postfix_index++] = ' ';
        top--;
    }
    postfix[postfix_index] = '\0';
    printf("\n");
}

// === 計算後序表達式 ===
double evaluate_postfix() {
	int i;
    numTop = -1;
    char *token = strtok(postfix, " ");
    
    printf("\n計算過程：\n");
    
    while(token != NULL) {
        printf("處理標記：'%s'\n", token);
        
        if(isdigit(token[0]) || (token[0] == '-' && isdigit(token[1]))) {
            double num = atof(token);
            numStack[++numTop] = num;
            printf("壓入數字：%.2f\n", num);
        }
        else if(is_operator(token[0])) {
            if(numTop < 1) {
                printf("錯誤：運算子 '%c' 缺少足夠的操作數\n", token[0]);
                exit(1);
            }
            double b = numStack[numTop--];
            double a = numStack[numTop--];
            double result = calculate(a, b, token[0]);
            numStack[++numTop] = result;
            printf("計算：%.2f %c %.2f = %.2f\n", a, token[0], b, result);
        }
        else {
            printf("錯誤：未知的標記 '%s'\n", token);
            exit(1);
        }
        
        printf("當前堆疊：");
        for(i = 0; i <= numTop; i++) {
            printf("%.2f ", numStack[i]);
        }
        printf("\n\n");
        
        token = strtok(NULL, " ");
    }
    
    if(numTop != 0) {
        printf("錯誤：計算結束後堆疊中剩餘 %d 個元素\n", numTop + 1);
        exit(1);
    }
    
    return numStack[numTop];
}

int main() {
    printf("請輸入中序表示式(支援+-*/^()運算) => ");
    
    fgets(input, MAX, stdin);
    input[strcspn(input, "\n")] = 0;
    
    printf("\n對應的後序表示法式： ");
    convert_to_postfix();
    double postfix_result = evaluate_postfix();
    printf("\n運算結果：%.2f", postfix_result);
    
    printf("\t(正確值為：");
    if(strcmp(input,"10+20*(50-30)/2^4-6*8")==0){
        printf("%g",10+20*(50-30)/pow(2,4)-6*8);
    }else if(strcmp(input,"10+20*(-50+30)/-2^4-6*8")==0){
        printf("%g",10+20*(-50+30)/pow(-2,4)-6*8);
    }else if(strcmp(input,"10.5+20.8*(50.1-30.6)/2.5^4-6.6*8.2")==0){
        printf("%g",10.5+20.8*(50.1-30.6)/pow(2.5,4)-6.6*8.2);
    }else if(strcmp(input,"10.5+20.8*(-50.1+30.6)/2.5^-4-6.6*8.2")==0){
        printf("%g",10.5+20.8*(-50.1+30.6)/pow(2.5,-4)-6.6*8.2);
    }
    printf(")");
    
    return 0;
}