题目：计算器 基本要求： 1.输入：不含变量的数学表达式的中缀形式，可以接受的操作符包括+、-、 *、/、%、(、)、√（选做）和x y（选做）。 2.输出：如果表达式正确，则输出表达式的结果，如果表达式非法，则输出 错误信息。用C语言写出代码

以下是一个简单的计算器的 C 语言代码，实现了加减乘除和括号的计算，支持整数和浮点数的运算，错误处理包括除数为零和非法表达式：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define MAX_SIZE 100

typedef enum { false, true } bool;

typedef struct {
    char data[MAX_SIZE];
    int top;
} Stack;

void init(Stack *s) {
    s->top = -1;
}

bool is_empty(Stack *s) {
    return s->top == -1;
}

bool is_full(Stack *s) {
    return s->top == MAX_SIZE - 1;
}

void push(Stack *s, char c) {
    if (is_full(s)) {
        printf("Stack overflow\n");
        exit(EXIT_FAILURE);
    }
    s->data[++s->top] = c;
}

char pop(Stack *s) {
    if (is_empty(s)) {
        printf("Stack underflow\n");
        exit(EXIT_FAILURE);
    }
    return s->data[s->top--];
}

char peek(Stack *s) {
    if (is_empty(s)) {
        printf("Stack underflow\n");
        exit(EXIT_FAILURE);
    }
    return s->data[s->top];
}

int priority(char c) {
    switch (c) {
    case '(':
        return 0;
    case '+':
    case '-':
        return 1;
    case '*':
    case '/':
    case '%':
        return 2;
    case '^':
        return 3;
    case '√':
        return 4;
    default:
        return -1;
    }
}

bool is_digit(char c) {
    return c >= '0' && c <= '9';
}

bool is_operator(char c) {
    return c == '+' || c == '-' || c == '*' || c == '/' || c == '%' || c == '^' || c == '√';
}

double evaluate(double a, char op, double b) {
    switch (op) {
    case '+':
        return a + b;
    case '-':
        return a - b;
    case '*':
        return a * b;
    case '/':
        if (b == 0) {
            printf("Divide by zero\n");
            exit(EXIT_FAILURE);
        }
        return a / b;
    case '%':
        if (b == 0) {
            printf("Divide by zero\n");
            exit(EXIT_FAILURE);
        }
        return (int)a % (int)b;
    case '^':
        return pow(a, b);
    case '√':
        return sqrt(a);
    default:
        printf("Invalid operator\n");
        exit(EXIT_FAILURE);
    }
}

double calculate(char *expr) {
    Stack op_stack, num_stack;
    init(&op_stack);
    init(&num_stack);
    double num = 0;
    bool has_dot = false;
    while (*expr != '\0') {
        if (*expr == ' ') {
            expr++;
            continue;
        }
        if (is_digit(*expr)) {
            num = num * 10 + (*expr - '0');
            if (has_dot) {
                num /= 10.0;
            }
        }
        else if (*expr == '.') {
            has_dot = true;
        }
        else if (is_operator(*expr)) {
            while (!is_empty(&op_stack) && priority(*expr) <= priority(peek(&op_stack))) {
                char op = pop(&op_stack);
                double b = pop(&num_stack);
                double a = pop(&num_stack);
                double result = evaluate(a, op, b);
                push(&num_stack, result);
            }
            push(&op_stack, *expr);
            num = 0;
            has_dot = false;
        }
        else if (*expr == '(') {
            push(&op_stack, *expr);
            num = 0;
            has_dot = false;
        }
        else if (*expr == ')') {
            while (!is_empty(&op_stack) && peek(&op_stack) != '(') {
                char op = pop(&op_stack);
                double b = pop(&num_stack);
                double a = pop(&num_stack);
                double result = evaluate(a, op, b);
                push(&num_stack, result);
            }
            if (!is_empty(&op_stack) && peek(&op_stack) == '(') {
                pop(&op_stack);
            }
            else {
                printf("Mismatched parentheses\n");
                exit(EXIT_FAILURE);
            }
            num = 0;
            has_dot = false;
        }
        else {
            printf("Invalid character\n");
            exit(EXIT_FAILURE);
        }
        expr++;
    }
    while (!is_empty(&op_stack)) {
        char op = pop(&op_stack);
        double b = pop(&num_stack);
        double a = pop(&num_stack);
        double result = evaluate(a, op, b);
        push(&num_stack, result);
    }
    if (num_stack.top == 0) {
        return num_stack.data[0];
    }
    else {
        printf("Invalid expression\n");
        exit(EXIT_FAILURE);
    }
}

int main() {
    char expr[MAX_SIZE];
    printf("Enter an expression: ");
    fgets(expr, MAX_SIZE, stdin);
    double result = calculate(expr);
    printf("Result: %g\n", result);
    return 0;
}