如果语句运行，即使不正确 [英] If statement running even when not true

问题描述

我不确定我在做什么错，每次运行它时，即使不是真的，它也会通过 if 部分?因此，"else"永远不会运行.

I am not sure what I'm doing wrong here, every time I run it, it goes through the if part even when it's not true? So the 'else' never runs.

#include <iostream>
using namespace std;

string choice;
float numb;

float convert(float numb,string choice)
{
    float newNo;
    if (choice == "F" or "f"){
        newNo = numb * 0.2 * 9 + 32;
    }else{
        newNo = (numb - 32) / 1.8;
    }
    return newNo;
}

int main()
{
    cout << "welcome to Temperature converter v0.1" << endl;
    cout << endl;
    cout << "Which conversion would you like to use?" << endl;
    cout << "type C to convert to Celsius and F to convert to Fahrenheit - ";
    cin >> choice;
    cout << "what number would you like to convert? - ";
    cin >> numb;

    cout << convert(numb,choice);


    return 0;
}

推荐答案

问题出在您的 if 语句:

if (choice == "F" or "f"){

基本上，您在这里说的是:如果选择是"F"或"f".您需要了解:除零( 0 )之外的所有内容都是真实的."f" 不为零，因此为true.您也可以输入( or = || ):

basically, what you say here is: If choise is "F" or if "f". You need to understand: True is everything besides zero (0). "f" is NOT zero, so it is true. You could also wirte (or = ||):

if (coice == "F" || true)

类似于:

if (true)

因此，为了使您的代码正常工作，您需要:

So in order for your code to work, you need:

if (choice == "f" || choice == "F")

那可以满足您的期望.

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