c - 制作计算器

Question

当我除以 2 个数字(10/2/2)时，如何才能得到正确的解决方案。另外，当一个数字除以另一个数字时，如何让它找到余数。

How would I begin with being able to divide by 2 or more numbers? With if-else statements.

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

void main()
{
    char operation = 0;
    double num1=0.0 ;
    double num2=0.0 ;
    printf("Enter the calculation\n");
    scanf("%f %c %f", &num1, &operation, &num2);

    switch (operation) {
    case '+':
        printf("= %f\n", num1 + num2);
        break;
    case '-':
        printf("= %f\n", num1 - num2);
        break;
    case '*':
        printf("= %f\n", num1*num2);
        break;
    case '/': 
        printf("= %f\n", num1 /(double)num2);
        break;
    case '%':
        printf("= %f\n", num1 % (double)num2);
        break;
    default:
        printf("Error!\n");
        break;
    }
    system("pause");
}

Answer 1

要获得您要查找的余数，您必须将两边都转换为 int:

    printf("= %d\n", (int)num1 % (int)num2);

要解析复杂的表达式，您需要完全不同的东西。现在您的代码只执行单个操作，因此可以忽略运算符优先级。但是当你进行链式操作时，你需要注意这一点。与 1 - 2 * 3 类似，您的代码应该执行 2*3，然后添加 1。最简单的方法是使用递归的解析器:http://en.wikipedia.org/wiki/Recursive_descent_parser

以下是基本/简单的规则概念:

line       -> expression <EOF>
expression -> factor + expression 
              factor - expression
              factor
factor     -> term * factor
              term / factor
              term % factor
              term
term       -> ( expression )
              <number>

然后，每个规则的代码看起来大致如下:

double read_factor(...) {
    double first = read_term(...);
    double second = 0.0;
    switch(peek_next_symbol()) {
    case '*': 
        consume_symbol();
        second = read_term();
        return first * second;
    case '/': 
        consume_symbol();
        second = read_term();
        if (second == 0)
            throw std::logic_error("div/0");
        return first / second;
    case '%': 
        consume_symbol();
        second = read_term();
        if (second == 0)
            throw std::logic_error("mod/0");
        return (double)((int)first % (int)second);
    default:
        return first;
    }
}

然后这个术语看起来隐约像这样:

double read_term() {
    double first = 0.0;
    switch(peek_next_symbol()) {
    case '(':
        consume_symbol();
        first = read_expression();
        if (peek_next_symbol() != ')')
            throw std::logic_error("missing )");
        consume_symbol();
    default:
        return read_number();
    }
}

我引用的每个函数都相对复杂，并且传递了大量的状态。现在我已经简要解释了该理论，这是一个很小的工作示例:http://ideone.com/wVqRw