Why wont my while loop take new input (c++)

Question

I've written a program to get a string input from a user and parse it into tokens and move a robot according to the input. My problem is trying to issue more than one command. The code looks like:

void Navigator::manualDrive()
{

    const int bufSize = 42;
    char uinput[bufSize];
    char delim[] = " ";
    char *token;
    while(true)
    {

        Navigator::parseInstruction(uinput);
    }
}  
/* parseInstruction(char *c) -- parses cstring instructions received
* and moves robot accordingly
*/


void Navigator::parseInstruction(char * c)
{

    const int bufSize = 42;
    char uinput[bufSize];
    char delim[] = " ";
    char *token;


    cout << "Enter your directions below: \n";
    cin.ignore();
     cin.getline (uinput, bufSize);


    token=strtok(uinput, delim);
    if(strcmp("forward", token) == 0)
    {
        int inches;
        token = strtok(NULL, delim);
        inches = atoi (token);
        Navigator::travel(inches);
    }
    if(strcmp("back",token) == 0)
    {
        int inches;
        token = strtok(NULL, delim);
        inches = atoi (token);
        double value = fabs(0.0735 * fabs(inches) - 0.0550);
        myRobot.backward(1/*speed*/, value/*time*/);
    }
    if(strcmp("turn",token) == 0)
    {
        int degrees;
        token = strtok(NULL, delim);
        if(strcmp("left",token) == 0)
        {
            token = strtok(uinput, delim);
            degrees = atoi (token);
            double value = fabs(0.0041 * degrees - 0.0523);
            myRobot.turnLeft(1/*speed*/, value/*time*/);
        }
    }
    if(strcmp("turn",token) == 0)
    {
        int degrees;
        token = strtok(NULL, delim);
        if(strcmp("right",token) == 0)
        {
            token = strtok(uinput, delim);
            degrees = atoi (token);
            double value = fabs(0.0041 * degrees - 0.0523);
            myRobot.turnRight(1/*speed*/, value/*time*/);
        }
    }
    if(strcmp("stop",token) == 0)
    {
        myRobot.motors(0,0);
    }
}

In the function manualDrive I have a while loop calling the function parseInstruction infinitely. The program outputs "Enter your directions below: " When I give the program instructions it executes them, and then it outputs "enter your directions below: " again and when I input my directions again it does not execute them and outputs "Enter your directions below: " instead. I'm sure this is a very simple fix I'm just very new to c++. So if you could please help me out and tell me why the program only takes the first set of directions. thanks

Answer 1

This sounds like the common issue that occurs when your cin command reads in the new line character from the previous input. I see that you have cin.ignore(), which is usually the fix for that problem, but it's still happening anyway.

Try moving your ignore to after the getline() command

Answer 2

You shouldn't need the cin.ignore() line here. cin.getline should already extract and discard the delimiter. I suspect it was throwing away the first character of your command. You can check this by changing your if statements to else-ifs and adding an else block at the end:

if(strcmp("forward", token) == 0)
else if(strcmp("back",token) == 0)
else if(strcmp("turn",token) == 0)
else if(strcmp("turn",token) == 0)
else if(strcmp("stop",token) == 0)
else
{
    std::cerr << "Unknown command '" << token << "'\n";
}

Answer 3

I believe your multiple if statements are part of the cause along with misreading the commands. I would also use the endl instead of using the /n char. Doing so means you don't need ignore.

void Navigator::manualDrive()
{

    const int bufSize = 42;
    char uinput[bufSize];
    char delim[] = " ";
    char *token;
    while(true)
    {

        Navigator::parseInstruction(uinput);
    }
}  
/* parseInstruction(char *c) -- parses cstring instructions received
* and moves robot accordingly
*/


void Navigator::parseInstruction(char * c)
{

    const int bufSize = 42;
    char uinput[bufSize];
    char delim[] = " ";
    char *token;


    cout << "Enter your directions below: " << endl;
    cin.getline (uinput, bufSize);


    token=strtok(uinput, delim);
    switch(token[3])//the command's fourth letter
    //needed letter because strings don't work with switch
    {
        case 'w': //forward
            int inches;
            token = strtok(NULL, delim);
            inches = atoi (token);
            Navigator::travel(inches);
            break;//this signifies the end of the case

        case 'k': //back
            int inches;
            token = strtok(NULL, delim);
            inches = atoi (token);
            double value = fabs(0.0735 * fabs(inches) - 0.0550);
            myRobot.backward(1/*speed*/, value/*time*/);
            break;

        case 'n': //turn
            int degrees;
            token = strtok(NULL, delim);
            if(strcmp("left",token) == 0)
            {
                token = strtok(uinput, delim);
                degrees = atoi (token);
                double value = fabs(0.0041 * degrees - 0.0523);
                myRobot.turnLeft(1/*speed*/, value/*time*/);
            }
            else if(strcmp("right",token) == 0)
            {
                token = strtok(uinput, delim);
                degrees = atoi (token);
                double value = fabs(0.0041 * degrees - 0.0523);
                myRobot.turnRight(1/*speed*/, value/*time*/);
            }
            break;

        case 'p': //stop
            myRobot.motors(0,0);
            break;

        default: //the default case
            cout << "Command Unknown" << endl;
            break;
    }
}