如果语句C＃则结束else

Question

I didn't know what else to use in this case but an if statement.

What I am trying to do is I am getting a value string direction; from a Windows form and checking if it has the value I am looking for. Then checking if the turtleDir which is a string value indicating the direction turtleDir has.

The problem comes here at else if statements, when the turtleDir is lookingleft it does all of the else if statements. What I want it to do is after it has done that else if statement it needs to stop and wait for the next command. not go through all the statements.

Can someone please advise me on how to fix it and what I am doing wrong?

Here is the code:

else if ( Program.form.direction == "right" ) 
{
   if ( turtleDir == "left" )
   {
      angle = -1.6f;
      turtleDir = "lookingLeft";
      Program.form.direction = "";
   }
   else if ( turtleDir == "lookingLeft" )
   {
      angle = 3.15f;
      turtleDir = "lookingDown";
   }
   else if ( turtleDir == "lookingDown" )
   {
      angle = 1.6f;
      turtleDir = "lookingRight";
   }
   else if ( turtleDir == "lookingRight" )
   {
      angle = 0.0f;
      turtleDir = "lookingUp";   
   }
}

Answer 1

You can use a switch statement on strings, too:

switch (turtleDir) {
    case "left":
        angle = -1.6f;
        turtleDir = "lookingLeft";
        Program.form.direction = "";
        break;
    case "lookingLeft":
        angle = 3.15f;
        turtleDir = "lookingDown";
        break;
    // other cases
}

This way, the switch block is always exited after your instructions are done. You can also specify what to do when the string matches none of these values by adding a case default: at the end. Remember each of these cases needs to be terminated by a break statement (or return / throw but i don't think you need those in this case).

If still every case is executed, your problem lies somewhere else. If a method contains this code and is called starting with eg turtleDir == "left" , each successive call of the method will let turtleDir cycle until every case has been executed and turtleDir ends up with the final value "lookingUp" . So look at your control flow and maybe keep track whether you already performed this check. Maybe keep track of the elapsed time and change turtleDir only if it has been in a particular state for a while (i don't know your requirements).

EDIT: You should set Program.form.direction = "" in every case statement. That's why your code gets executed over and over again. Also, if no direction is entered, clear it, too.

Answer 2

You can use an empty return; - Statement, but then you leave your method too...

Answer 3

Use a switch

switch (turtleDir)
{
    case "left":
        angle = -1.6f;
        turtleDir = "lookingLeft";
        Program.form.direction = "";
        break;

    case "lookingLeft":
        angle = 3.15f;
        turtleDir = "lookingDown";
        break;

    case "lookingDown":
        angle = 1.6f;
        turtleDir = "lookingRight";
        break;

    case "lookingRight":
        angle = 0.0f;
        turtleDir = "lookingUp";   
        break;

    default:
        // Optional, but place any actions if non of the above is matched
        break;
}

Answer 4

There is something else going on here....

Only one branch of an IF/ELSE-IF statement will be executed. You might want to refactor to a SWITCH statement for readability reasons; but not because it would change your behaviour .

Look at this code:

    if(0 == 0) { Console.WriteLine("Branch 1"); }
    else if(true==true) { Console.WriteLine("Branch 2"); }
    else if(false==false) { Console.WriteLine("Branch 3"); }

ALL of the conditions are true. And the first one executes. ONLY the first one.

In this code - only the second two are true: if(0 == 2) { Console.WriteLine("Branch 1"); } else if(true==true) { Console.WriteLine("Branch 2"); } else if(false==false) { Console.WriteLine("Branch 3"); }

And ONLY the second one executes.

A series of else-if's won't all execute if the condition is true.

My guess is that you are looping through this really fast or something and the next iteration is entering the IF logic and executing the next branch. You might need to post more code so that you get more helpful answers for your particular situation.

The best way to track this down, IMHO, is to just place a breakpoint on the start of your IF logic and step-through the code one execution at a time. You should see that it only goes into one ELSE-IF branch and exits, and you can see if/why it re-enters.

Finally, the SWITCH statement doesn't allow you to implicitly execute multiple branches either.

    switch(test)
    {
        case "one":
            Console.WriteLine("Branch 1");
        case "two":
            Console.WriteLine("Branch 2");
    }

That won't even compile. I believe in C/C++ you could fall though case statements unless you explicitly added break; or similar control statement. In C# that's not the case.