中缀表达式a+b*c+(d*e+f)*g，其转换成后缀表达式则为abc*+de*f+g*用栈实现代码c语言

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

char stack[MAX];
int top = -1;

void push(char item) {
    if (top >= MAX - 1) {
        printf("Stack Overflow\n");        return;
    }
    stack[++top] = item;
}

char pop() {
    if (top < 0) {
        printf("Stack Underflow\n");
        exit(1);
    }
    return stack[top--];
}

int is_operator(char symbol) {
    if (symbol == '^' || symbol == '*' || symbol == '/' || symbol == '+' || symbol == '-') {
        return 1;
    } else {
        return 0;
    }
}

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

void infix_to_postfix(char infix[], char postfix[]) {
    int i, j;
    char item;
    char x;

    push('(');
    strcat(infix, ")");
    i = 0;
    j = 0;
    item = infix[i];

    while (item != '\0') {
        if (item == '(') {
            push(item);
        } else if (isdigit(item) || isalpha(item)) {
            postfix[j] = item;
            j++;
        } else if (is_operator(item) == 1) {
            x = pop();
            while (is_operator(x) == 1 && precedence(x) >= precedence(item)) {
                postfix[j] = x;
                j++;
                x = pop();
            }
            push(x);
            push(item);
        } else if (item == ')') {
            x = pop();
            while (x != '(') {
                postfix[j] = x;
                j++;
                x = pop();
            }
        } else {
            printf("Invalid infix Expression.\n");
            exit(1);
        }
        i++;

        item = infix[i];
    }
    if (top > 0) {
        printf("Invalid infix Expression.\n");
        exit(1);
    }
    postfix[j] = '\0';
}

int main() {
    char infix[MAX], postfix[MAX];

    printf("Enter Infix expression : ");
    gets(infix);

    infix_to_postfix(infix, postfix);
    printf("Postfix Expression: ");
    puts(postfix);

    return 0;
}

--相关问题--:
1. 什么是中缀表达式和后缀表达式？
2. 除了栈，还有