It must be simple, but i can't seem to find the explanation. Why does the following generates these errors:
Unreachable code detected (on result++)
WindowsFormsApplication1.Form1.GetResult(int, int): not all code paths return a value
private int GetResult(int start, int end)
{
for (int result = start; result < end; result++)
{
return result;
}
}
Anyone who could please help me out? Thnx in advance :)
EDIT:
First of all, thanks for the many (fast) replys. Stupid of mine...but i didn't see it.
And sorry, i needed to be a little more precise of what it is i wanted to accieve..
I need a method that adds 1 to a value (result) starting from the given start value (int start) untill it reaches another value (int end).
So it might also add directly to start integer if I’m not mistaking. And return that value?
Because your method is returning an int type, and the compiler can't determine whether you will get inside the loop.
What if the result is greater than or equal to end, in that case, the statement inside the loop will not execute and hence you get the error.
From MSDN - For Loop
Because the test of a conditional expression occurs before the
execution of the loop, a for statement executes zero or more times.
This gives you the reason behind the error "not all code path returns a value", because if the for loop executes 0 times then the method will not return anything
For warning "Unreachable code detected", the reason is that your update expression result++ executes after the execution of the for block. Since your for block contains return statement, you will never reach your update expression
What a clever compiler!
for (int result = start; result < end; result++)
{
return result;
}
... is equivalent to:
int result = start;
while(result < end) {
return result;
result++;
}
If start >= end as we go into this code, the content of the while loop will never run. In that case, the program flow won't hit a return statement: Not all code paths return a value.
If start < end as we enter the function, the program flow will go into the loop, hit the return statement, and the method will return. It can't hit the result++ statement. Unreachable code detected.
In response to your edit:
public int getResult(int start, int end) {
int result = start;
while(result < end) {
result++;
}
return result;
}
... does what you describe. However it's a wasteful way to get that result. If start=0 and end=1000000, the program will loop a million times.
You'd get exactly same result more efficiently with:
public int getResult(int start, int end) {
if(end > start) {
return end;
} else {
return start;
}
}
Or even:
public int getResult(int start, int end) {
return Math.Max(start,end);
}
(Although it's still not clear what you want the result to be if start > end)
There are two different cases at the beginning of the method:
Case start < end: You always return result immediately in the
first loop run. Therefore result is never going to be incremented.
Case start >= end: You never enter the loop, therefore you'd need
another return statement outside of it.
It is obvious that result++ is unreachable. You would reach it after the first execution of the loop, if any - but in this very first execution of the loop, you return, thus exiting the function.
For the second part of the question, see Habib's answer.
private int GetResult(int start, int end)
{
int result = 0;
for (result = start; result < end; result++)
{
return result;
}
return result;
}
This way the function should work.
You are calling the for loop.
It sets result=start compares if condition is true
and then returns result.
How shall it ever reach result++ ?
=Unreachable code detected (on result++)
could be that the loop never enters when result > end so
=not all code paths return a value
lets assume that the condition "result < end" is true. The control will then go the statement inside the loop. Since it is a return statement, control will come out of the function/method GetResult. So, the control never reaches to "result++". That is why you get - unreachable code.
Let me know, if it is useful.
All the best !!!
If you add a return statement after the for loop it will compile without errors.
private int GetResult(int start, int end)
{
int result = 0;
for (result = start; result < end; result++)
{
return result;
}
return result;
}
This function returns start if start < end, else it doesn't return anything.
What was the intention of your method ?
Let us consider a scenario in which your condition result < end got failed . so the control
will not enter into loop and will come out of loop. but outside there is no return statement so what would it return as other end is expecting some integer to be return , so that's why you are getting error.
this will work :-
private int GetResult(int start, int end)
{
for (int result = start; result < end; result++)
{
return result;
}
return 0;
}
if the start > end value ,the code inside the loop will never be executed and hence there wont be anything to return from the function and hence you will get those errors.
Moreover there is no point of using for loop as u did since in the first step itself if start
private int GetResult(int start, int end)
{
if(start<end)
return start;
return -1;
}
I don't think for and return do what you think they do. As I read your code, it could be dumbed down to this:
private int GetResult(int start, int end)
{
if (start < end)
{
return start;
}
else
{
return 0; // or another default for when start >= end
}
}
Because return will, well, return from the method. Since the first iteration of the loop (if start < end) will immediately return result, which has been set to the value of start.
As your code shows, the else part is missing. Therefore the compiler doesn't know what you want to return when start >= end and also result++ is never called because you directly return, so it'll throw the error and warning shown.
Because if start >= end, the loop will not be entered
private int GetResult(int start, int end)
{
for (int result = start; result < end; result++)
{
return result;
}
return -1; // Path here exists
}
Out of interest, if you want to return each of the integers between start and end, you should look at yield return instead:
private IEnumerable<int> GetResult(int start, int end)
{
for (int result = start; result < end; result++)
{
yield return result;
}
// Now we don't need a return, because the loop will eventually complete
}
Edit Looking at the comments, OP may well want a sequence of numbers.
The above method can be iterated
foreach (int anInt in GetResult(40, 50))
{
Console.WriteLine(string.Format("Next value is {0}", anInt));
}
Related
public void OnPressHigher()
{
if (min >= max || guess == max) return;
min = guess + 1;
NextGuess();
}
I can't figure out what is returned in this if statement.
There is nothing returned because your functions return type is void. In the context in your code it means that if the condition min >= max || guess == max isn't met, the function shouldn't continue to execute and should return to it's caller.
The method is declared as returning void
public void OnPressHigher()
Which means it will never return anything.
Therefore, a return instruction will simply exit the method at that point and not execute any further instructions within the method.
I just learned Method Declaring and i don't know too much how to use it, i tried to make an algorithm that takes 2 numbers and return their smallest common divide, and if there is no common divider, return -1, thats the code:
class Program
{
static int Div(int a, int b)
{
int max = Math.Max(a, b);
bool div = false;
for(int i = 2; i <= max / 2; i++)
{
if (a % i == 0 && b % i == 0)
{
return i;
div = true;
i = max;
}
}
if (div == false)
{
return -1;
}
}
static void Main(string[] args)
{
Console.WriteLine("Please Enter 2 Numbers");
int num = int.Parse(Console.ReadLine());
int num2 = int.Parse(Console.ReadLine());
Console.WriteLine(Div(num, num2));
}
}
it tells me that there is an unreachable code, and not all code paths return a value, but why? if i get 2 numbers that does have a commong divider it will return it, and if not it will return -1, no execptions I think, thanks in advance
The compiler is not clever enough. But the last if is redundant anyway because it's always false there, so you can write following which also avoids the compiler error:
static int Div(int a, int b)
{
int max = Math.Max(a, b);
for (int i = 2; i <= max / 2; i++)
{
if (a % i == 0 && b % i == 0)
{
return i;
}
}
return -1;
}
The part after the return in the loop was unreachable and unnecessary, so i've removed it.
When you use return you exit the function immediately, no code beyond that line will execute therefore the lines after aren't reachable.
return i;
div = true; <<
i = max; <<
In your case, seems like you just want to set those values before you return.
if (a % i == 0 && b % i == 0)
{
return i;
div = true;
i = max;
}
The 2 lines after the return are never reached. Put them before the return. Also I don't think you need a div bool at all. It's redundant and can be optimized away.
Proving whether an arbitrary method can reach the end of the method without hitting a return or throwing an exception is provably an unsolvable problem. You can always construct a method such that the compiler would be unable to prove whether or not the endpoint is reachable, if you try hard enough. However, it's important for the compiler to not allow any programs that have a return value but no reachable endpoint.
As a consequence of this, there are false positives. The compiler does it's best to determine if a program has a reachable endpoint, and if it fails to prove it, it will error, even if you and I both know that the endpoint isn't actually reachable.
You'll need to change your code such that the compiler is able to prove that the endpoint isn't reachable, and the easiest way to do that is to remove the if (div == false) line and just always return -1;. You and I know that div will never be true there, but the compiler isn't sophisticated enough to prove it.
The return in the first if clause in the for loop is before the rest of the code, so there are 2 lines of code that will never get hit, these 2:
div = true;
i = max;
The reason they'll never get hit is because if the if statement is true, it'll immediately return, and if it's false it'll go to the second if.
2 reasons : The line div=true is unreachable, the code after return is not executed. Replace
return i;
div = true;
i = max;
by
int res=i;
div = true;
i = max;
return res;
And the last 'if' clause has no 'else' clause allowing to return in all cases;
I'm fairly new to coding (especially c#) - this is an assignment for a programming fundamentals class - I'm not looking for the answer - I'm looking for someone to explain why I get these two 'error's for a boolean method I'm supposed to create to check if the user's guess for a letter or the full word in a game of hangman.
The errors I get are - 'Unreachable Code detected - for the idx++ part - which doesn't make sense as I've used it in other separate methods..
And Program.CheckGuess(char[], char[], char[], string: not all code paths return a value.
I know I'm not fully finished the aspect. It's probably staring at me in the face - just looking for some guidance. Thanks.
static bool CheckGuess(char[] secrets, char[] mask, char[] letters, string guess)
{
int misses = 0; bool condition = false;
for (int idx = 0; idx < secret.Length; idx++)
{
guess.ToCharArray();
if (mask[idx] == guess[idx])
{
//reveal character or word
condition = true;
}
else
{
misses = misses + 1;
condition = false;
}
return condition;
}
}
You should understand that a return statement, when executed, makes the control jump out of the method and back to the caller.
In your code, your return is statement is placed inside the for loop. When an iteration of the for loop is executed, the control jumps out of the method immediately and goes back to the caller of the method.
As you know, the last part in a for loop header (idx++) is executed when an iteration has finished executing. However, in your case, an iteration will never finish because it just jumps back to the caller when control reaches return. This is why the first error occurred.
You should also understand that every method which doesn't have void as the return type needs to return no matter what.
So what if the for loop's condition (the middle part) is never true? The for loop will never be executed, right? If the for loop isn't executed, then what should the method return?
The error says that not all code path returns a value because the method would not return if the for loop isn't executed.
To fix this, you just need to move the return statement out of the for loop:
static bool CheckGuess(char[] secrets, char[] mask, char[] letters, string guess)
{
int misses = 0; bool condition = false;
for (int idx = 0; idx < secret.Length; idx++)
{
guess.ToCharArray();
if (mask[idx] == guess[idx])
{
//reveal character or word
condition = true;
}
else
{
misses = misses + 1;
condition = false;
}
}
return condition;
}
Because you have a return statement.
When this return inside your for loop is reached, the program jumps out of the loop and thus makes you i++ unreachable.
i want to write following for loop by using C# Recursion please guide me . Thank you !
StringMobileNo = value.ToString();
for (int i = 0; i < 3; i++)
{
if (StringMobileNo.StartsWith("0"))
{
StringMobileNo = StringMobileNo.Remove(0, 1);
}
}
If you want to recursively remove leading zeroes, you can do this:
public string RemoveZeroes(string input)
{
if (!input.StartsWith("0"))
return input;
return RemoveZeroes(input.Remove(0, 1));
}
An explanation:
Check if there are leading zeroes.
If not, simply return the input string.
If so, remove the first zero and then recur, calling the same method with the first character removed.
This will cause the method to recur until, finally, there are no leading zeroes, at which point the resulting string - with all leading zeroes removed - will be returned all the way up the call stack.
Then call like so:
var myString = RemoveZeroes(StringMobileNo);
However, the same can be achieved by simply doing:
StringMobileNo.TrimStart('0');
Note that I have assumed here that the i < 3 condition is an arbitrary exit condition and you actually want to remove all leading zeroes. Here's one that will let you specify how many to remove:
public string RemoveZeroes(string input, int count)
{
if (count < 1 || !input.StartsWith("0"))
return input;
return RemoveZeroes(input.Remove(0, 1), count - 1);
}
You don't need recursion at all for that.
Instead, use TrimStart to remove all leading 0
StringMobileNo.TrimStart('0')
I think you don't need to use Recursion function here.
you can Use String.TrimStart("0") but if you want to use Recursion function
Try This:
class Program
{
static void Main(string[] args)
{
Recursion("000012345",0);
}
static void Recursion(string value,int c)
{
String MobileNo = value;
int count=c;
if (MobileNo.StartsWith("0") && count<3)
{
count++;
Recursion(MobileNo.Remove(0, 1),count);
}
}
}
I have been up half the night and still trying to get this null exception figured out. I have read a few of texts about this issue but none has helped me in any way, to me what the problem is as it should work :/ It just crashes at this piece of code:
Private void UpdateGUI()
{
string selectedItem = cmbDisplayOptions.Items[cmbDisplayOptions.SelectedIndex].ToString();
rdbtReserv.Checked = true;
lstReservations.Items.Clear();
lstReservations.Items.AddRange(m_seatMngr.GetSeatInfoStrings(selectedItem));
}
lstReservations.Items.AddRange(m_seatMngr.GetSeatInfoStrings(selectedItem)); Gives me the ArgumentNullExeption, but to me it should not do that.
the addrange sends string selectedItem to another class:
public string[] GetSeatInfoStrings(string selectedItem)
{
int count = GetNumOfSeats(selectedItem);
if (count <= 0)
{
return null;
}
string[] strSeatInfoStrings = new string[count];
for (int index = 0; index <= m_totNumOfSeats - 1; index++)
{
strSeatInfoStrings[index] = GetSeatInfoAt(index);
}
return strSeatInfoStrings;
}
This int count = GetNumOfSeats(selectedItem); goes to here and returns with an int:
private int GetNumOfSeats(string selectedItem)
{
if (selectedItem == "ReservedSeats")
{
return GetNumReserved();
}
if (selectedItem == "VacantSeats")
{
return GetNumVacant();
}
else
{
return m_totNumOfSeats;
}
}
I have checked the arrayed have the correct number of spaces(60) and that selectedItem has a string(Allseats to start with so it should return m_totnumOfSeats which is an int of 60) But then in the private int GetNumOfSeats something goes wrong and it returns null and...well why?
I can't see the problem.. maybe gone blind by trying to find the issue. Always got outstanding help here and I have learned tons!! So maybe someone can point out all the issues there is in my code.
Thanks a million in advance for any and all advice!
//Regards
Check if your variables are actually initialized and returns correct values.
There are logical errors in the GetSeatInfoStrings methods and the GetNumofSeats method.
Lucky for you the GetNumOfSeats method will always return 60 for you because of the wrong way you compare strings. It's not the right way, so use the Equals method for comparison like
if (selectedItem.Equals("ReservedSeats"))
With that you will get a proper output form GetNumOfSeats(string) method.
The next thing is to fix your looping in the GetSeatInfoStrings method so as to not get an array index out of bounds exception like this.
string[] strSeatInfoStrings = new string[count];
for (int index = 0; index <= count; index++)
{
strSeatInfoStrings[index] = GetSeatInfoAt(index);
}
return strSeatInfoStrings;
Also fix the part where your logic returns a null in the GetSeatInfoStrings method. it should return an empty string array according to your logic as
return new string[0];
That should probably get your methods working. You need to be very careful of what you code before you debug it :-)
Looking at the source code of ObjectCollection, when you call AddRange and pass a null value, you get back the ArgumentNullException.
You could prevent this changing this code
if (count <= 0)
{
return new string[0];
}