While loop multiple condition check with single variable

Question

I am wondering if there is a way to check multiple while loop conditions using the same variable. That's a bit vague, but this example should clear it up:

while (myFunction(x) == 0 || myFunction(x) == 13639 || myFunction(x) == -4261.9583)
{ x++; }

Is it possible to only evaluate myFunction(x) once per loop while checking the three conditions, so that the function doesn't have to run three separate times for a result that is the same each time?

I am doing this for optimization/efficiency purposes. myFunction() could be a pretty time-consuming function, so I want it to run the minimum amount of times necessary.

Typically I would define the value of myFunction(x) before I start the while loop, but in this case, the value of myFunction(x) will be changing as the loop goes through each iteration, since the value of x will be changing.

You can extract it to a function. It would fulfill your requirements and also would be better in terms of code transparency - the name of the function will self-explain the meaning of these currently "magic" numbers like 0, 13639, -4261.9583. — Yeldar Kurmangaliyev
– Yeldar Kurmangaliyev, Commented May 7, 2019 at 17:52
I concur with @YeldarKurmangaliyev he is right, extract it to a function; for example a bool return would suffice... Also can you show the code for myFunction()? You are already doing something I would assume... — Trevor
– Trevor, Commented May 7, 2019 at 17:54

Heinz Kessler · Accepted Answer · 2019-05-07 17:57:02Z

4

Yes, this can be done:

double result;
while ((result = myFunction(x)) == 0 || result == 13639 || result == -4261.9583)
{ x++; }

answered May 7, 2019 at 17:57

Heinz Kessler

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1 Comment

Xiaoy312 Over a year ago

You can also declare the variable inline in recent version of C# (7?): while (myFunction(x) is var result && (result == 0 || result == 13639 || result == -4261.9583))

John Wu · Accepted Answer · 2019-05-08 09:46:51Z

Three options:

Do it backwards

Check a list for the result rather than checking the result against the list.

var list = new float[] { 0F, 13639F, -4261.9583F );
while (list.Contains(myFunction(x))
{
    x++;
}

Write a function

Extracting the logic to another function is always a nice way to break down the problem.

bool IsValid(float input)
{
    var result = myFunction(input);
    return (result == 0 || result == 13639 || result == -4261.9583);
}

while (IsValid(x))
{ 
    x++;
}

Use `while(true)`

Whenver the condition of a while loop is complicated, a common option is to remove the check from the () and put it in the {} instead. When you do this, use while (true).

while (true)
{
    var result = myFunction(x);
    if (result != 0 && result != 13639 && result != -4261.9583) break;
    x++;
}

bassfader · Accepted Answer · 2019-05-07 17:55:49Z

1

You can do this simply by moving the check into a separate method, which takes the return value of the function as parameter, and then performs the 3 checks on the value directly and returns a boolean accordingly.

Assuming the function returns a int typed value this may for example look something like this:

bool CheckResultValue(int value) {
    return value == 0 || value == 13639 || value == -4261.9583;
}

Then your while loop could look something like this:

while (CheckResultValue(myFunction(x)))
{ x++; }

answered May 7, 2019 at 17:55

bassfader

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While loop multiple condition check with single variable

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Do it backwards

Write a function

Use `while(true)`

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Do it backwards

Write a function

Use while(true)

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Use `while(true)`