I'm trying to make a program that finds the factors of a number. I made a fairly simple one but it always repeated the same two factors twice i.e. 1 and 2, 2 and 1. So, to fix that I tried to check if the number had been used before but it keeps saying the bool proceed is unassigned.
using System;
namespace FactorableOrNah
{
class MainClass
{
public static void Main (string[] args)
{
Console.WriteLine ("Enter a whole number to view its factors: ");
int userInput = int.Parse(Console.ReadLine ());
int[] antiDoubler = new int[userInput];
bool proceed;
Console.Clear();
for (int i = 1; i != userInput; i++) {
antiDoubler[i] = userInput / i;
for(int j = 0; j < userInput; j++) {
if (antiDoubler [j] == i)
proceed = false;
else
proceed = true;
}
if ((userInput % i) == 0 && i != 1 && proceed == true)
Console.WriteLine("{0} and {1}", i, (userInput / i));
}
}
}
}
Using uninitialized variables in C# is not allowed. The compilation error can be solved by using either:
bool proceed = false;
or
bool proceed = default(bool);
since the default value of bool is false;
However, the algorithm is too complicated and very hard to read. Just for fun. A recursive example.
static IEnumerable<int> GetFactors(int number)
{
return GetFactors(number, number);
}
static IEnumerable<int> GetFactors(int number, int check)
{
if (check > 0)
{
if (number % check == 0)
{
yield return check;
}
foreach (var f in GetFactors(number, --check))
{
yield return f;
}
}
}
UPDATE:
Local variables cannot be left uninitialized, however class members (static members and instance variables), furthermore array elements are initialized automatically by the memory manager, so they are never uniitialized.
From the specification:
A variable must be definitely assigned (ยง5.3) before its value can be
obtained. As described in the following sections, variables are either
initially assigned or initially unassigned. An initially assigned
variable has a well-defined initial value and is always considered
definitely assigned. An initially unassigned variable has no initial
value. For an initially unassigned variable to be considered
definitely assigned at a certain location, an assignment to the
variable must occur in every possible execution path leading to that
location.
For your case you have an initially unassigned variable. Thus, the variable must be set in every possible execution path. There is one possible execution path to which your variable is not defined - when userInput >= j.
This would happen if userInput is 0. Following your program manually:
The first for case will check if i != userInput. Since i = 1 this is true, thus it will continue in the for loop.
the second for case will check if j < userInput. Since j = 0 this is false, thus it will skip the for case and never set proceed
Now you have arrived to where you check proceed and it was never set. So the compiler tells you that this is not allowed.
To solve your issue, you have to decide whether to:
define a default value for proceed, for instance false and set it at declaration, i.e. bool proceed = false;.
Rewrite your logic so that you do not need the boolean, for instance like Daniel Leiszen suggests.
Related
Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 6 years ago.
Improve this question
I am currently trying to define two integer variables by user input. If the user inputs an integer which is not contained in the defined range, the user will be asked to input again, until the user inputs an accepted value.
static void Main(string[] args)
{
int a;
int b;
bool isAValid = false;
bool isBValid = false;
while (isAValid == false)
{
Console.Write("Input number from 2 to 20: ");
isAValid = true;
a = Convert.ToInt16(Console.ReadLine());
if (a < 2 || a > 20)
{
isAValid = false;
}
}
while (isBValid == false)
{
Console.Write("Input number from 2 to 20: ");
isBValid = true;
b = Convert.ToInt16(Console.ReadLine());
if (b < 2 || b > 20)
{
isBValid = false;
}
}
}
What I am trying to accomplish, is saving the user input as a and b respectively, so the local variable value is defined as the user input value. However, when I try to access the local variable after the last while loop is broken, I get the "Use of unassigned local variable a (or b)".
Any ideas how I can define the variables, while still having the input prompt loop?
It's funny that the compiler cannot see that the while loops are always entered, and a and b are always initialized.
Update: Eric Lippert commented that for the purpose of flow control analysis all expressions involving variables are considered possibly true or false; even expressions like x*0 == 0.
We see that the while condition is always true, partly because we know this little logic pattern for input. We know what the loop is about. The compiler doesn't. It sees an arbitrary condition and can't be bothered to prove that it is always true. It simply considers all expressions with variables non-constant.
One way to fix this is to express the logic of the program better in the language. Such a pattern is not uncommon: "Repeat something until a condition is satisfied". In particular, do it at least once in any case. There is a language construct for that in all C family languages: The do/while loop. Rewriting the loop for a gives
do
{
Console.Write("Input number from 2 to 20: ");
isAValid = true;
a = Convert.ToInt16(Console.ReadLine());
if (a < 2 || a > 20)
{
isAValid = false;
}
} while (isAValid == false);
Now I can access a after the loop; the compiler recognizes that the assignment will be guaranteed. The same should work for b.
This also enables us to write less cluttered code. The ancillary variable isAValid is needed only because of the "artificial" test when the while loop is first entered. The test is artificial because we do not have any input yet and hence cannot really test anything. If we indeed test only after the input, so that test data is available, we can put the test right into the condition. It boils down to
do
{
Console.Write("Input number from 2 to 20: ");
a = Convert.ToInt16(Console.ReadLine());
} while (a < 2 || a > 20);
To fix your error, declare this:
int a = 0;
int b = 0;
Instead of:
int a;
int b;
This will initialized your local variables and will fix your error message.
How to get value in conditional statement in c# (example in a if statement and you want the value in the if statement be used outside it ) how?
example
int a, b, c;
if (a > 3)
{
c = 20;
}
else if (b < 3)
{
c = 10;
}
//how do i get the value of c outside the conditional statement??
Console.WriteLine("{0}", c);
//it always says local variable unassigned local variable
*update supposedly my code is correct and i
ve declared a; and i want to use the value of a outside the conditional statement.
*update all i want to know is to get the value of c outside the conditional
It seems you declared a but didn't initialize it.In C# you should initialize local variables to something before the first usage. If your if statement evaluates to false then a will remain uninitialized.And even if it would evalute to true you are trying to read its value (in x++) before initializing it, so it will still be a problem. To fix that just initialize it with a default value while declaring:
int a = 0;
In this case a should be declared outside the if statement. IE
int a = 1;
if(condition){
a=a++;
}
console.WriteLine("{0}",a);
However, there are several issues with your code. Most notably, are you sure you want to be doing a=a++? This code is redundant, you should be doing just a++.
I suspect your real issue lies outside the code you shared. If you post more code I can refine my answer to help you more.
In your new code example, the problem is that you've declared variables a, b, and c but have not initialized them. An if statement might be entered and it might not be entered so any assignments done inside of an if statement might not be executed.
You need to tell the compiler what the initial values of a, b and c are before you can use them, which I think almost everyone here has already been saying. Try changing your code to this:
int a = 0, b = 0, c = 0;
if (a > 3)
{
c = 20;
}
else if (b < 3)
{
c = 10;
}
//This should print out 10
Console.WriteLine("{0}", c);
//no more compile errors will occur
Notice that a, b, and c have been given default values of 0 so in the event that the if statement is not entered, they will still be assigned a usable value.
Also, if a = 0 and b = 4 then the entire if block is skipped, leaving c untouched which is where its default value of 0 will be printed to the console.
Another option, which isn't the best thing to do in my opinion is the following
int a = 0, b = 0, c;
if (a > 3)
{
c = 20;
}
else if (b < 3)
{
c = 10;
}
else
{
c = 1;
}
Console.WriteLine("{0}", c);
This will compile even though you're not initializing the c variable because in a round about way you are; in the final else the variable is assigned 1 so there would be no case were c is not initialized.
Your problem is not c at all; your problems are a and b. You just need a bit more understanding how the compiler works.
Let's put it this way: you have...
int a, b, c;
Here, you're telling the compiler that it will use 3 variables that somewhere, eventually, will contain int values; but now they don't have nothing, they're empty (note: not 0; empty) or as known in C#, they're null.
When the compiler reaches here:
if (a > 3)
{
c = 20;
}
it says: "whoops! I need to check if a is less than 3, but before this line a is never assigned a value, it's empty, and I can't check it like that. I'll better throw an error."
Same happens with the next condition.
If, as other answers say, before the condition you assign them a value, the compiler will be able to compare and use them.
Now let's take a look at your original code:
int a;
//I'll asume you declared a the same way that the other code
if (condition)//this is true
{
a = a++;
}
//how do i get the value of a?
Console.WriteLine("{0}", a);
//it always says local variable unassigned local variable
When the compiler reaches to Console.WriteLine("{0}", a);, it says: "Hmmm... I have to print a, but it has a value only if conditionis true, but if it is false, I won't be able to print it because it'll be empty. Better throw an error now than when running!"
As you see, is all about using your variables only after you're sure that all possible ways that lead to your line of code assign a value to that variable.
I'm trying to find out if a number is prime or not. But I've got an error of "unreachable code detected", which I think is effecting the error of "not all code paths return a value". The error seems to occur in the for loop at i++. Can anyone help me please?
static void Main(string[] args)
{
Console.WriteLine(isPrime(10));
}
public static bool isPrime(int n)
{
for (int i = 2; i < n; i++)
{
if (n % i == 0)
{
return false;
}
return true;
}
}
"Unreachable code detected" means that some code can never be executed. Consider:
int something()
{
if (true)
return 1;
else
return 2; //Obviously we can never get here
}
"Not all code paths return a value" means that you've defined a method with a return value (like "bool" in your example) and there is some way for the method to execute without returning a value.
Consider:
int something(bool someBool)
{
if (someBool)
return 1;
//if someBool == false, then we're not returning anything. Error!
}
Your code has two problems:
You have return true inside the for loop (outside of any conditional). Because return immediately exits the function (returning control to the caller) the i++ statement of the for loop will never get executed (hence your bug). You likely intended for that to be outside the for loop.
Another problem with that being in the loop is that the loop is not guaranteed to execute. If the n passed was 2 or less, you would skip the loop entirely, and there is no return statement in that case. This isn't allowed (since you always need to return a value from a non-void function) so you get a compiler error.
Below is an example of how to get this return working with a for loop and embedded If condition.
private bool WinOneLevelOne()
{
//For loop to check all the items in the winOne array.
for (int i = 0; i < winOne.Length; i++)
{
//If statement to verify that all the gameobjects in the array are yellow.
if (winOne[i].gameObject.GetComponent<MeshRenderer>().material.color != Color.yellow)
{
//Keeps the boolean at false if all the gameobjects are not yellow.
return false;
}
}
return true;
Visual Studio keeps saying Use of unassigned variable for iVal and iNumber. Can anyone tell me where I'm going wrong?
This is designed to be a code to ask the user to keep entering integers and adding them up until the user wants to stop. The sum of the integers is then displayed on the console.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace AddFive
{
class Program
{
static void Main(string[] args)
{
int iNumber;
int iVal;
int iTotal = 0;
while (iVal > 0)
{
Console.WriteLine("Enter number " + iNumber);
iVal = Convert.ToInt32(Console.ReadLine());
iTotal = iTotal + iVal;
}
if (iNumber <= 0)
{
Console.WriteLine("Total = " + iTotal);
iVal = Convert.ToInt32(Console.ReadLine());
iTotal = iTotal + iVal;
}
Console.WriteLine("Total = " + iTotal);
Console.WriteLine();
Console.WriteLine("Press any key to close");
Console.ReadKey();
}
}
}
Assign values to those variables. You need to assign values to local variables before using them
int iNumber = 0;
int iVal = 0;
when you wrote while (iVal > 0), the value of iVal has not been set
You can get away with that only with instance/class variable, as they are initialized to default value
public class Program
{
int i; //this was not implicitly initialized to zero (0)
public Program()
{
int j; //need to initialize this before use
Console.Write(j); //this throws "Use of unassigned variable" error
Console.Write(i); //this prints 0, the default value
}
}
Visual Studio is correct, you're trying to reference an uninitialized variable.
Try this:
int iNumber = 0;
int iVal = 0;
This way, your are initializing the variables to an initial value of 0.
The original problem occurs on these lines:
while (iVal > 0)
and
if (iNumber <= 0)
In which you try to access the variables before giving them a value.
In C# you must assign value to variable before use it.
e.g.
int iNumber = 0;
int iVal = 0;
You need to initialize iNumber and iVal. Think about what value they will have the first time through the while loop, in your current code.
Your iVal parameter is unassigned in your while loop. you need to give is a value when you initialize it.
The issue is as noted in several places that you do not assign a value to iNumber or iVal before you use them the first time (in your while statements). In this particular case it's benign and assigning the default value what change a thing. The error is though appropriate. Historically unassigned variables have been a headache in languages that do allow the use of unassigned variables. Especially in languages that do not initialize a storage location to default value. C# does initialize to a default value in this case but it might still lead to hard to find bugs. The compiler is smart enough to check the path the code takes before reaching a particular use of a local and if you can get there with out assigning a value it will complain. This can help in complex code where the code when read sequentially leads you to think that the local has been assigned but in fact due to conditional logic it's not
I know this is a very newbie C# question but I am implementing a small program which does the following:
namespace ConsoleApplication
{
class Program
{
static void Main(string[] args)
{
bool isRun = false;
int number = 0;
while (isRun = (true) && number < 3)
{
++number;
Console.WriteLine("Number = {0}", number.ToString());
Console.WriteLine();
}
Console.WriteLine(isRun.ToString());
Console.ReadLine();
}
}
}
At the end of the while loop, I would have expected the bool value to be true, but is is printed to be false. Why is that? Is this different from C++ where I would have done something like and the same thing in C# is giving me false
while(number<3)
{
is = true;
}
if(is){
cout<<true;
}
The reason you're seeing this behavior is due to the operator precedence involved. Here the && binds more strongly than = so the code in the loop is actually bound as the following
while (isRun = (true && number < 3)) {
...
}
Once number > 3 the && expression is false and is assigned into the isRun value and simultaneously terminates the loop. Hence once the loop exits you will see isRun as false
To get the behavior you are looking for you will need to manually correct the precedence with parens.
while ((isRun = (true)) && number < 3) {
...
}
Note: In general, as #Servey pointed out, the assignment of locals to expressions inside the loop predicate is considered bad practice. Many C# users would actually be surprised that code compiles at all because they've been conditioned to only use == in loops.
It's more idiomatic to simply set isRun to true on the first line of the loop for this pattern.
while (number < 3) {
isRun = true;
...
}
The problem is that you have set you boolean variable to false and without assigning it back to true, in while loop you are matching it against the value true, thus it fails in every case.