Why does it give the same output for every value? - c++

Question

int main (void)
{
char n;
label0:
cout<<"Please enter a character value(C/S)\n";
cin>>n;
n = toupper(n);
if ( n!= 'C' || n!= 'S' )
{
cout<<"Please enter proper value\n";
cin.clear();
cin.ignore();
goto label0;
}
else
{
cout<<"You entered"<<n<<"\n";
}
return 0;
}
In this code, even when I enter c C s S , it gives the same output as Please enter the proper value. Why is it not comparing?

Answer 1

if ( n!= 'C' || n!= 'S' )
This is true for every n in the world. You probably meant to use &&.
Think about it:
if n == 'C', then the condition is satisfied since n != 'S',
if n == 'S', then the condition is satisfied since n != 'C',
if n == 'X', then the condition is satisfied since n != 'C',
...
Read more about short circuit evaluation.

Answer 2

In general, you are having trouble by understanding the way in that logical operators are used.
The condition n != 'C' is equivalent to !(n == 'C').
Thus, the if() condition in your code can be rewritten in this way:
if ( !(n == 'C') || !(n == 'S') )
However, the condition you need in your code is another one:
if ( ! (n == 'C' || n == 'S') )
I suggest to do the job in reverse order:
if ( n== 'C' || n== 'S' )
{
cout<<"You entered"<<n<<"\n";
}
else
{
cout<<"Please enter proper value\n";
cin.clear();
cin.ignore();
goto label0;
}
In this way, if the entered character is c C s S, then the character is correct, and in any other case, a new character must be entered.
On the other hand, the goto statements must be used only in excepcional cases, when the flow of the program becomes very intrincated, and one really need "to jump out of the mess".
However, your program is very simple, and can be achieved with normal loop control sentences, such as do {} while():
int main (void)
{
char n;
do {
cout<<"Please enter a (proper) character value(C/S)\n";
cin>>n;
n = toupper(n);
cin.clear();
cin.ignore();
} while ( ! (n == 'C' || n == 'S') );
cout<<"You entered"<<n<<"\n";
return 0;
}
Now, the user is enforced to enter one of the desired characters: c C s S, until the entered character is correct.