command-line calculator in c

命令行计算器在C语言中通常是一个简单的程序，它允许用户通过终端输入数学运算指令并获取结果。这个程序会读取用户的输入，解析出操作符和操作数，然后计算并显示结果。以下是创建一个基础的命令行计算器的一个简单示例：

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

// 定义基本的运算函数
double add(double a, double b) {
    return a + b;
}
double subtract(double a, double b) {
    return a - b;
}
double multiply(double a, double b) {
    return a * b;
}
double divide(double a, double b) {
    if (b != 0)
        return a / b;
    else
        return "Error! Division by zero is not allowed.";
}

int main() {
    char op; // 运算符
    double num1, num2;

    printf("Enter first number: ");
    scanf("%lf", &num1);
    printf("Enter operator (+, -, *, /): ");
    scanf(" %c ", &op); // 确保只接收字符，忽略空格
    printf("Enter second number: ");
    scanf("%lf", &num2);

    switch(op) {
        case '+':
            printf("%.2lf + %.2lf = %.2lf\n", num1, num2, add(num1, num2));
            break;
        case '-':
            printf("%.2lf - %.2lf = %.2lf\n", num1, num2, subtract(num1, num2));
            break;
        case '*':
            printf("%.2lf * %.2lf = %.2lf\n", num1, num2, multiply(num1, num2));
            break;
        case '/':
            printf("%.2lf / %.2lf = %.2lf\n", num1, num2, divide(num1, num2));
            break;
        default:
            printf("Invalid operator!\n");
    }

    return 0;
}