#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();
double evaluate_infix(char *expr);
double parse_number(char **expr);

// === 檢查運算子優先順序 ===
//int get_priority(char op) {
//    switch(op) {
//        case '+': case '-': return 1;
//        case '*': case '/': return 2;
//        case '^': return 3;
//        default: return 0;
//    }
//}

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;
    }
}

// === 解析數字（包括浮點數） ===
double parse_number(char **expr) {
    char *end;
    double result = strtod(*expr, &end);
    *expr = end;
    return result;
}

// === 轉換為後序表達式 ===
void convert_to_postfix() {
    int i = 0 , j;
    int postfix_index = 0;
    top = -1;
     
//    printf("後序表示法：");
    
    while(input[i] != '\0') {
        if(isdigit(input[i]) || input[i] == '.' || (input[i] == '-' && (i == 0 || input[i-1] == '(' || is_operator(input[i-1])))) {
            char *end;
            double num = strtod(&input[i], &end);
            int len = end - &input[i];
            printf("%.1f ", num);
            for(j = 0; j < len; j++) {
                postfix[postfix_index++] = input[i+j];
            }
            postfix[postfix_index++] = ' ';
            i += len - 1;
        }
        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])) {
            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];
}

// === 直接計算中序表達式 ===
double evaluate_infix(char *expr) {
    char opStack[MAX];
    double valStack[MAX];
    int opTop = -1;
    int valTop = -1;
    
    printf("\n中序計算過程：\n");
    
    while(*expr) {
        if(isspace(*expr)) {
            expr++;
            continue;
        }
        
        if(isdigit(*expr) || *expr == '.' || (*expr == '-' && (valTop == -1 || opStack[opTop] == '('))) {
            double num = parse_number(&expr);
            valStack[++valTop] = num;
            printf("壓入數字: %f\n", num);
        }
        else if(*expr == '(') {
            opStack[++opTop] = *expr++;
            printf("壓入左括號\n");
        }
        else if(*expr == ')') {
            printf("處理右括號\n");
            while(opTop >= 0 && opStack[opTop] != '(') {
                char op = opStack[opTop--];
                double b = valStack[valTop--];
                double a = valStack[valTop--];
                valStack[++valTop] = calculate(a, b, op);
                printf("計算: %f %c %f = %f\n", a, op, b, valStack[valTop]);
            }
            if(opTop >= 0) opTop--;  // 移除左括號
            expr++;
        }
        else if(is_operator(*expr)) {
            while(opTop >= 0 && opStack[opTop] != '(' && 
                  (get_priority(opStack[opTop]) > get_priority(*expr) ||
                   (get_priority(opStack[opTop]) == get_priority(*expr) && *expr != '^'))) {
                char op = opStack[opTop--];
                double b = valStack[valTop--];
                double a = valStack[valTop--];
                valStack[++valTop] = calculate(a, b, op);
                printf("計算: %f %c %f = %f\n", a, op, b, valStack[valTop]);
            }
            opStack[++opTop] = *expr++;
            printf("壓入運算子: %c\n", *(expr-1));
        }
        else {
            expr++;  // 跳過未知字符
        }
    }
    
    while(opTop >= 0) {
        char op = opStack[opTop--];
        double b = valStack[valTop--];
        double a = valStack[valTop--];
        valStack[++valTop] = calculate(a, b, op);
        printf("計算: %f %c %f = %f\n", a, op, b, valStack[valTop]);
    }
    
    return valStack[valTop];
}

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(")");
    
//    printf("\n=== 中序直接計算 ===\n");
//    double infix_result = evaluate_infix(input);
//    printf("中序計算結果：%f\n", infix_result);
    
    return 0;
}