C语言：中缀表达式求值

中缀表达式求值需要使用栈来实现，以下是C语言实现中缀表达式求值的代码示例：

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

#define MAX_STACK_SIZE 100

int stack[MAX_STACK_SIZE];
int top = -1;

void push(int value) {
    if (top >= MAX_STACK_SIZE - 1) {
        printf("栈已满\n");
        exit(1);
    }
    top++;
    stack[top] = value;
}

int pop() {
    if (top < 0) {
        printf("栈已空\n");
        exit(1);
    }
    int value = stack[top];
    top--;
    return value;
}

int is_operator(char c) {
    return c == '+' || c == '-' || c == '*' || c == '/';
}

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

int evaluate(char* expression) {
    int i, num, num1, num2;
    char c, op;

    for (i = 0; expression[i] != '\0'; i++) {
        c = expression[i];
        if (isdigit(c)) {
            num = 0;
            while (isdigit(c)) {
                num = num * 10 + c - '0';
                i++;
                c = expression[i];
            }
            i--;
            push(num);
        } else if (is_operator(c)) {
            if (top < 1) {
                printf("表达式错误\n");
                exit(1);
            }
            num2 = pop();
            num1 = pop();
            op = c;
            switch (op) {
                case '+':
                    push(num1 + num2);
                    break;
                case '-':
                    push(num1 - num2);
                    break;
                case '*':
                    push(num1 * num2);
                    break;
                case '/':
                    push(num1 / num2);
                    break;
            }
        }
    }

    if (top != 0) {
        printf("表达式错误\n");
        exit(1);
    }

    return pop();
}

int main() {
    char expression[100];
    int result;

    printf("请输入中缀表达式：\n");
    scanf("%s", expression);

    result = evaluate(expression);

    printf("结果为：%d\n", result);

    return 0;
}

运行程序后，会提示用户输入中缀表达式，然后根据运算符优先级计算结果并输出。