Input

This is a discussion on Input within the C++ Programming forums, part of the General Programming Boards category; I'm new at C++ code and don't understand how to get a program to take a full line of input ...

  1. #1
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    Input

    I'm new at C++ code and don't understand how to get a program to take a full line of input from the user. I was looking in the tutorial, but it only explains how to use variables to accept one character or integer, as opposed to taking a full word. Please help.

    EDIT- I apologize. I found it.
    Last edited by Foley; 08-27-2006 at 11:29 AM. Reason: Never mind.

  2. #2
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    C++ has a library called <string>. the data type string can hold any number of characters. eg,
    Code:
    #include <iostream>
    #include <string>
    using namespace std;
    
    int main()
    {
        string s = "Hello, World!";
        cout << s;
    }
    To get a full line of text from the user, to be stored in a string, use the getline() function.
    Code:
    #include <iostream>
    #include <string>
    using namespace std;
    
    int main()
    {
        string s;
        cout << "Enter input: \n";
        getline(cin, s);
        cout << "User inputted: " << s << endl;
    }

  3. #3
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    One more question: How can I make an If with a string?

    ie, I want to a certain thing to happen if the user enters a certain string.

    Thanks.

  4. #4
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    You can make an if with a C++ string the same way as with any other type, eg,
    Code:
    #include <iostream>
    #include <string>
    using namespace std;
    
    int main()
    {
        cout << "Would you like to hear a joke?" << endl;
        string response;
        getline(cin, response);
        if ( "yes" == response )
            cout << "Two Parrots are sat on a perch.  One says to the other "
                 << "\"Can you smell fish?\"" << endl;
        cout << "Goodbye";
    }
    Just be careful that strings, like char's are case-sensitive. ie, "yes" is not the same as "YES"

  5. #5
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    Thank you guys SO much. I'm working on a text based game and this is a great help.

  6. #6
    すまん Hikaru's Avatar
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    Quote Originally Posted by Foley
    ie, I want to a certain thing to happen if the user enters a certain string.
    It's easy if you want an exact match. Just compare the string variable with a quoted string.
    Code:
    #include <iostream>
    #include <string>
    
    using std::cout;
    
    int main()
    {
        std::string command;
    
        cout << "Do you want a <greeting> or do you want to <quit>: ";
    
        if (cin >> command)
        {
            if (command == "greeting")
            {
                cout << "Hello!\n";
            }
            else if (command == "quit")
            {
                cout << "Goodbye\n";
            }
            else
            {
                cout << "I don't understand\n";
            }
        }
    
        return 0;
    }
    It's probably better to search for a substring though, that way if you type in some spaces or something, the messages still work.
    Code:
    #include <iostream>
    #include <string>
    
    using std::cout;
    using std::string;
    
    int main()
    {
        string command;
    
        cout << "Do you want a <greeting> or do you want to <quit>: ";
    
        if (getline(std::cin, command))
        {
            if (command.find("greeting") != string::npos)
            {
                cout << "Hello!\n";
            }
            else if (command.find("quit") != string::npos)
            {
                cout << "Goodbye\n";
            }
            else
            {
                cout << "I don't understand\n";
            }
        }
    
        return 0;
    }

  7. #7
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    Okay, one more question. I'm having a little trouble with loops.

    I want to loop an effect that says if something happens, something else happens, ie:

    Code:
        while (z==1){
    
        string command;
    
        getline(cin, command);
    
              if ( "attribute"||"att" == command) {
    
                   cout<<"Your current attributes are:\n";
    
                   cout<<"Strength: "<<s<<"\n";
    
                   cout<<"Dexterity: "<<d<<"\n";
    
                   cout<<"Intelligence: "<<i<<"\n";
    
                   cout<<"Wisdom: "<<w<<"\n";}
                   };
    This is an excert from the game I'm making. I have z set to always equal 1. The problem is that I want it to loop that while z=1, if you type attribute or att you will see the attributes. But it loops that no matter what you type it shows the attributes. I don't understand why it's doing this. Please help.
    Last edited by Foley; 08-27-2006 at 06:59 PM.

  8. #8
    すまん Hikaru's Avatar
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    Quote Originally Posted by Foley
    if ( "attribute"||"att" == command) {
    That's the problem, and I think it's because the left side of the || expression is saying "do this if the string isn't a null pointer". I'm sure that a quoted string will never be null, so the if always returns true because || expressions are short circuited. It returns as soon as a true result is found. This is what you want instead, I think.
    Code:
    if (command == "attribute" || command == "att")

  9. #9
    (?<!re)tired Mario F.'s Avatar
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    You have two problems...
    First, if ( "attribute"||"att" == command) doesn't work. Without entering into much detail about lvalues and rvalues, how you should create these type of conditions is:

    if ( "attribute" == command || "att" == command)


    The second problem is:
    When z == 1 you enter a loop. That loop first reads your input. If the input is either "attriute" or "att", it will display the current attributes.

    Now... What happens next? When it finishes displaying the attributes, z will still be == 1. So the loop will repeat from the start. It will wait again for an input from you. If you don't input "attribute" or "att", the if statement will return false. So no attributes will be displayed and once again z was unchanged. Which means once again it will go to the beggining of the loop and wait for another input from you.

    Without more info of what z means, I have little advice to give you. But the main thing here is that your loop is being controlled by a variable that is never changing. So you entered an infinite loop. You need to either change z inside the loop or reevaluate your code and ask yourself if you really need that loop. Maybe this will be enough:
    Code:
        string command;
    
        getline(cin, command);
    
              if ( 1 == z && "attribute" == command || "att" == command) {
    
                   cout<<"Your current attributes are:\n";
    
                   cout<<"Strength: "<<s<<"\n";
    
                   cout<<"Dexterity: "<<d<<"\n";
    
                   cout<<"Intelligence: "<<i<<"\n";
    
                   cout<<"Wisdom: "<<w<<"\n";}
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  10. #10
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    The problem is that I want it to loop that if that is the command, then the attributes show, and otherwise the program continues as normal. Instead, it loops that if it doesn't get the command, it waits for it. I want the loop to be there, but in the background.
    Last edited by Foley; 08-29-2006 at 12:28 PM.

  11. #11
    Registered User major_small's Avatar
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    just be careful with the substring thing... take 'quit' for example... say somebody says
    "why dont' you quit your dayjob?"
    that code will exit them from the program

    or what about
    "quit greeting me like that!"

    is that a response to your greeting, or is it them wanting to quit? or something else?

    this is stretching slightly into AI concepts, and if you keep it to old-school Mud style you shouldn't have a problem with it. Just do a google search for "Mud" and you'll see that nerds are more powerful than wet pools of dirt... so HA!

    menus are very nice too
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  12. #12
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    Okay, I tried something a little different to see if I could get what I want.

    Code:
    while (z==1) {
        string command;
        getline(cin, command);
                if ( 1 == z && "attribute" == command || "att" == command) {
                  cout<<"Your current attributes are:\n";
                  cout<<"Strength: "<<s<<"\n";
                  cout<<"Dexterity: "<<d<<"\n";
                  cout<<"Intelligence: "<<i<<"\n";
                  cout<<"Wisdom: "<<w<<"\n";}
                else {
    The object was that if you typed attribute or att you got your attributes, and if you put anything else, you get the other text. Everything else was behind "else". And the program did not appriciate it. It gave me an endless stream of everything else in the game instead of the attributes- and when I went up top looked, the attributes had never even been displayed. How in the world did that happen?

  13. #13
    Frequently Quite Prolix dwks's Avatar
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    Watch your precedence. I think you might want to change this:
    Code:
    if ( 1 == z && "attribute" == command || "att" == command) {
    ->
    Code:
    if ( 1 == z && ( "attribute" == command || "att" == command ) ) {
    dwk

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