要支持多位小数的情况，可以对代码进行适当修改。以下是修改后的代码：

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

#define MAX_SIZE 100

// 定义栈结构
typedef struct {
    double data[MAX_SIZE];
    int top;
} Stack;

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

int isEmpty(Stack *s) {
    return s->top == -1;
}

void push(Stack *s, double value) {
    if (s->top >= MAX_SIZE - 1) {
        printf("栈已满，无法入栈！\n");
        exit(1);
    }
    s->data[++(s->top)] = value;
}

double pop(Stack *s) {
    if (isEmpty(s)) {
        printf("栈已空，无法出栈！\n");
        exit(1);
    }
    return s->data[(s->top)--];
}

double peek(Stack *s) {
    if (isEmpty(s)) {
        printf("栈已空，无法取栈顶元素！\n");
        exit(1);
    }
    return s->data[s->top];
}

double calculate(double a, char operator, double b) {
    switch(operator) {
        case '+':
            return a + b;
        case '-':
            return a - b;
        case '*':
            return a * b;
        case '/':
            if (b == 0.0) { // 处理除数为零的情况
                printf("除数不能为零！\n");
                exit(1);
            }
            return a / b;
        default:
            printf("非法运算符！\n");
            exit(1);
    }
}

double evaluate(char *expression) {
    Stack operandStack; // 操作数栈
    Stack operatorStack; // 运算符栈

    initStack(&operandStack);
    initStack(&operatorStack);

    int i = 0;
    while (expression[i] != '\0') {
        if (isdigit(expression[i])) { // 处理数字字符
            double num = 0.0;
            while (isdigit(expression[i]) || expression[i] == '.') {
                if (expression[i] == '.') {
                    i++;
                    break;
                }
                num = num * 10 + (expression[i] - '0');
                i++;
            }

            double decimal = 0.1;
            while (isdigit(expression[i])) {
                num += decimal * (expression[i] - '0');
                decimal /= 10.0;
                i++;
            }

            push(&operandStack, num);
        } else if (expression[i] == '+' || expression[i] == '-' || expression[i] == '*' || expression[i] == '/') { // 处理运算符
            while (!isEmpty(&operatorStack) && peek(&operatorStack) != '(' && ((expression[i] == '*' || expression[i] == '/') ||
                  ((expression[i] == '+' || expression[i] == '-') && (peek(&operatorStack) == '+' || peek(&operatorStack) == '-')))) {
                char op = pop(&operatorStack);
                double b = pop(&operandStack);
                double a = pop(&operandStack);
                double result = calculate(a, op, b);
                push(&operandStack, result);
            }
            push(&operatorStack, expression[i]);
            i++;
        } else if (expression[i] == '(') { // 处理左括号
            push(&operatorStack, expression[i]);
            i++;
        } else if (expression[i] == ')') { // 处理右括号
            while (!isEmpty(&operatorStack) && peek(&operatorStack) != '(') {
                char op = pop(&operatorStack);
                double b = pop(&operandStack);
                double a = pop(&operandStack);
                double result = calculate(a, op, b);
                push(&operandStack, result);
            }
            if (!isEmpty(&operatorStack) && peek(&operatorStack) == '(') {
                pop(&operatorStack); // 弹出左括号
            } else {
                printf("括号不匹配！\n");
                exit(1);
            }
            i++;
        } else if (expression[i] == ' ') { // 处理空格
            i++;
        } else { // 非法字符处理
            printf("非法字符！\n");
            exit(1);
        }
    }

    while (!isEmpty(&operatorStack)) {
        char op = pop(&operatorStack);
        double b = pop(&operandStack);
        double a = pop(&operandStack);
        double result = calculate(a, op, b);
        push(&operandStack, result);
    }

    return peek(&operandStack); // 返回最终结果
}

int main() {
    char expression[MAX_SIZE];

    printf("请输入中缀表达式：");
    fgets(expression, sizeof(expression), stdin);

    // 将输入的字符串去掉末尾的换行符
    if (expression[strlen(expression)-1] == '\n') {
        expression[strlen(expression)-1] = '\0';
    }

    double result = evaluate(expression);

    printf("计算结果：%lf\n", result);

    return 0;
}

修改后的代码在处理数字字符时支持多位小数，通过识别小数点进行处理。其他部分保持不变。


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