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While loop is not exiting

htown (26)
string cmd;
cout << "skynet@2.0: ";
cin >> cmd;
while(cmd != "Exit" || cmd != "EXIT" || cmd != "exit")
{
cout << "skynet@2.0: ";
cin >> cmd;
if(cmd == "help" || cmd == "HELP" || cmd == "Help")
help_cmd();
cout << "skynet@2.0: ";
cin >> cmd;

if (cmd == "version" || cmd == "Version" || cmd == "VERSION")
version_cmd();

if (cmd == "Date" || cmd == "date" || cmd == "DATE")
date_cmd();

else
cout << "Invaild command." << endl;
}
Aramil of Elixia (772)
post the whole code. urs is messy but it should work
htown (26)
#include <string>
#include <iostream>
using namespace std;

void help_cmd();
void version_cmd();
void date_cmd();

int main()
{
cout << "Welcome to Skynet 2.0!" << endl << endl;
string cmd="";
while(cmd != "Exit" || cmd != "EXIT" || cmd != "exit")
{
cout << "skynet@2.0: ";
cin >> cmd;
if(cmd == "help" || cmd == "HELP" || cmd == "Help")
help_cmd();

if (cmd == "version" || cmd == "Version" || cmd == "VERSION")
version_cmd();

if (cmd == "Date" || cmd == "date" || cmd == "DATE")
date_cmd();

else
cout << "Invaild command." << endl;

}
cout << "Have a nice day! Goodbye.";
return 0;
}

void help_cmd()
{
cout << "help - Display list of all commands with description" << endl;
cout << "version - Displays current version " << endl;
cout << "date - Display current date or change to new date" << endl;
cout << "exit - exit out of program " << endl;
}

void version_cmd()
{
cout << "The current version is 2.0" << endl;
}

void date_cmd()
{
cout << "date";
}
Aramil of Elixia (772)
try this:

while(true)
{
getline(cin, cmd);
//other features
if(cmd == "exit")
break;
}

i dont know whats wrong with urs though it can be written better
DesiredNote (238)
I'm not sure why it isn't working. It really doesn't make any sense. >_>
You should just do what the other user suggested until I, or another member, find working solution.
Last edited on
htown (26)
ok thanks so much!
DesiredNote (238)
while(cmd != "exit" && cmd != "EXIT" && cmd != "Exit")
I should have really noticed this, and I apologize for that. You don't want to use the || operator, you want to use the && operator. That should fix the problem.

Here is your fixed code.
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#include <string>
#include <iostream>
using namespace std;

void help_cmd();
void version_cmd();
void date_cmd();

int main()
{
    cout << "Welcome to Skynet 2.0!" << endl << endl;
    string cmd;
    while(cmd != "exit" && cmd != "EXIT" && cmd != "Exit")
    {
        cout << "skynet@2.0: ";
        cin >> cmd;
        if(cmd == "help" || cmd == "HELP" || cmd == "Help")
            help_cmd();

        else if(cmd == "version" || cmd == "Version" || cmd == "VERSION")
            version_cmd();

        else if(cmd == "Date" || cmd == "date" || cmd == "DATE")
            date_cmd();
    }
    cout << "Have a nice day! Goodbye.";
    return 0;
}

void help_cmd()
{
    cout << "help - Display list of all commands with description" << endl;
    cout << "version - Displays current version " << endl;
    cout << "date - Display current date or change to new date" << endl;
    cout << "exit - exit out of program " << endl;
}

void version_cmd()
{
    cout << "The current version is 2.0" << endl;
}

void date_cmd()
{
    cout << "date";
}
Last edited on
Aramil of Elixia (772)
no thats wron... i tested and it works but why does || logic not work?
Disch (13742)
i tested and it works but why does || logic not work?


Remember that || returns true if either the right or left side of it is true

And the while loop will keep looping as long as the condition is true.

So given the below:

while(cmd != "Exit" || cmd != "EXIT")

this means the loop will keep going if
cmd != "Exit" OR cmd != "EXIT".

Which means the only way for the loop to exit would be if both of those conditions are false... which means cmd would have to be both "Exit" and "EXIT" -- which is impossible.

Example:

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cmd = "Exit";

while(cmd != "Exit" || cmd != "EXIT")
while(   false      ||    true      ) // <- doesn't match "EXIT"
while(             true             ) // <- keep going

//..... another.....

cmd = "EXIT";

while(cmd != "Exit" || cmd != "EXIT")
while(    true      ||    false     ) // <- doesn't match "Exit"
while(             true             ) // <- keep going
Aramil of Elixia (772)
oh..... i feel like an idiot. logic can be very confusing sometimes
DesiredNote (238)
I really should have explained how that works. :F
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