If always returns true [duplicate]

I'm just experimenting a bit with C++ but I can't figure out why both if-statements return true:

#include <iostream>
#include <windows.h>
using namespace std;

int main()
{
    cout << "Language?" << endl;
    string lang;
    cin >> lang;
    if(lang == "Deutsch" || "deutsch")
    {
        cout << "Hallo Welt!";
    }
    else
    {
        return false;
    }
    if(lang == "English" || "english")
    {
        cout << "Hello World!";
    }
    else
    {
        return false;
    }
    return 0;
}

I'm pretty new to C++ and stackoverflow so I'm sorry if that's an stupid or frequently asked question but I really don't know any further. Please help!

Solution 1:

 lang == "Deutsch" || "deutsch"

is wrong

lang == "Deutsch" || lang == "deutsch"

is right

"deutsch" alone returns the address of the string in memory. which is always not equal to zero. which means true.

a == "hello" || "bob"

means

(a == "hello") || "bob"

regardless of what a == "hello" results in (true or false), false || "bob" becomes false || pointer to "bob". All non-null pointers are true, so this is false || true which is true.

#include <iostream>
#include <windows.h>
using namespace std;

int main()
{
    cout << "Language?" << endl;
    string lang;
    cin >> lang;
    if(lang == "Deutsch" || lang == "deutsch")
    {
        cout << "Hallo Welt!";
    }
    else
    {
        return false;
    }
    if(lang == "English" || lang == "english")
    {
        cout << "Hello World!";
    }
    else
    {
        return false;
    }
    return 0;
}

Solution 2:

The expression lang == "Deutsch" || "deutsch" is actually equivalent to (lang == "Deutsch") || ("deutsch"). The second part of the expression is a const char* with a non-zero value, which means it will evaluate to true. The same applies to your second if statement.

You meant to write lang == "Deutsch" || lang == "deutsch".

Solution 3:

The sentence:

if(lang == "Deutsch" || "deutsch")

is interpreted by the compiler as this:

"IF lang is equal to "Deutsch" OR the memory address of the string "deutsch" is not equal to 0 THEN...

Remember that in C/C++ any expression that is not zero, is considered to be TRUE. The expression "deutsch" is a string constant, which as an expression, returns its starting address, which is likely not 0.