#include <stdio.h>
#include <stdlib.h>
#define MAX 50 
char infix_q[MAX];
int compare(char stack_o , char infix_o);
void infix_to_postfix();



int get_priority(char c){
	if(c=='+' || c=='-'){
		return 1;
	}else if(c=='*' || c=='/'){
		return 2;
	}else if(c=='^'){
		return 3;
	}else{
		return 0;
	} 
}

int main(){
	int i=0;
	for(i=0;i<MAX;i++){
		infix_q[i]='\0';
	}
	printf("\t--------------------------------------------\n");
	printf("\t中序運算式轉換成後序運算式\n");
	printf("\t可以使用的運算子包括:^,*,+,-,/,(,) 等\n");
	printf("\t--------------------------------------------\n");
	printf("\t請輸入中序運算式\n");
	infix_to_postfix();
	printf("\n");
	return 0;
}


int compare(char stack_o,char infix_o){
//	char infix_priority[9]={'#',')','+','-','*','/','^',' ','('};
//	char stack_priority[8]={'#',')','+','-','*','/','^',' '};
	int index_s = 0 ,index_i = 0;
	while(stack_priority[index_s]!=stack_o){
		index_s++;
	}
	while(infix_priority[index_i]!=infix_o){
		index_i++;
	}
	return index_s/2 >= index_i/2 ? 1 : 0;
}


void infix_to_postfix() {
    int rear = 0, top = 0, flag = 0, i = 0;
    char stack_t[MAX];
    int tag = 1;
    for(i = 0; i < MAX; i++) {
        stack_t[i] = '\0';
    }
    

    fgets(infix_q, MAX, stdin);
    infix_q[strcspn(infix_q, "\n")] = 0;
    
    i = 0;
    while(infix_q[i] != '\0') {
        i++;
        rear++;
    }
    infix_q[rear] = '#';
    printf("\t後序表示法：");
    stack_t[top] = '#';
    
    for(flag = 0; flag <= rear; flag++) {
    	tag = 1;
        switch(infix_q[flag]) {
            case ')':
                while(stack_t[top] != '(') {
                    printf("%c", stack_t[top--]);
                }
                top--;
                break;
            case '#':
                while(stack_t[top] != '#') {
                    printf("%c", stack_t[top--]);
                }
                break;
            case '(':
            case '*':
            case '/':
            case '^':
            	while(compare(stack_t[top], infix_q[flag]) == 1) {
                    printf("%c", stack_t[top--]);
                }
                stack_t[++top] = infix_q[flag];
                break;
            case '+':
            case '-':
                if(tag==1){
                	while(compare(stack_t[top], infix_q[flag]) == 1) {
                    	printf("%c", stack_t[top--]);
                	}
                	stack_t[++top] = infix_q[flag];
                	break;
				}else if(tag==2){
					
				}
                
                
            default:
                if(infix_q[flag] != ' ') {  // 忽略空格
                    printf("%c", infix_q[flag]);
                }
                break;
        }
    }
}