Why can't I redefine this variable in C++? - c++

Question

char x;
bool tf;
void IsNumber(char x)
{
switch (x)
{
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
case '0':
bool tf(true);
break;
default:
bool tf(false);
break;
}
}
int main(int argc, const char * argv[])
{
using namespace std;
cout << "Test if a character is a number: " << endl;
char x;
cin >> x;
IsNumber((char) x);
if (bool tf = true)
cout << "True" << endl;
if (bool tf = false)
cout << "False" << endl;
return 0;
}
I am getting an error after the default: saying I can't redefine the variable. Also, it says, at the bottom, that I the variable tf isn't a variable. I am really new to C++, I only know python can someone help me out?
New code giving me an error:
#include <iostream>
bool tf;
tf = true;
bool IsNumber(char x)
{
switch (x)
{
case '1':

Answer 1

You're trying to declare two variables with the same name in the same scope. The switch statement itself defines a scope, but each case clause does not. If you want a scope within a case clause, then you'll have to provide one yourself:
case '0':
{
bool tf(true);
break;
}
Although it's not clear what good that is; you're declaring a local variable then ignoring it. Perhaps you meant to set the global variable:
case '0':
tf = true;
break;
so you could then check it with
if (tf) // NOT if (bool tf = true) - that also declares a new local variable
or, less freakily, perhaps you want to return a value:
bool IsNumber(char x) {
switch (x) {
case '0':
// and so on
return true;
default:
return false;
}
}
and test it with
if (IsNumber(x)) {
cout << "True" << endl;
} else {
cout << "False" << endl;
}
or, if verbosity isn't your thing
cout << (IsNumber(x) ? "True" : "False") << endl;
or even
cout << boolalpha << IsNumber(x) << endl;
You should probably take some time to read an introductory book until you're comfortable with the basics such as scopes, declarations and definitions. Here are some recommendations.

Answer 2

You haven't assigned anything to tf, for comparison operators we want =='s instead of just the ='s.
if (tf == true) {
}

Answer 3

You can only define a variable one you can assign it as many times as you need.
bool tf = false
means I am define a variable and assigning it
if I just want to assign it later
tf = false
if I want to do a conditional test
if (tf){do stuff}

Answer 4

You have x defined at the very top as a global variable, and then try and define it again in main. You have to pick one or the other, or rename one. What you probably want to do is get rid of the one in main.
You also have your bools compared as = instead of how they should be like ==.
Edit: You actually don't need the comparison in there at all.
if(tf){
cout << "True\n"
}
else cout << "False\n"
That will see if tf is true and output true and if not, output false.