CodeGym/Help with Java Tasks/Why can't i declare multiple int variables on the same li...

Level 41

26.08.2020
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Why can't i declare multiple int variables on the same line, inside the function?

Question about the task

Sum of the digits of a three-digit number

Under discussion

Hello, I have the following code but when I debug the code I get the following error: "java: variable sum might not have been initialized" Why I am not allowed to declare int variables sum and m in the same row using the formula " int sum, m = 0". The only way it is accepted is by declaring them individually;

public static int sumDigitsInNumber(int number) {
       int sum, m = 0;
      //rest of code

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Guadalupe Gagnon

Level 37 , Tampa, United States

27 August 2020, 13:49

useful

This error is caused because you are using the variable sum somewhere in your code before it has been initialized. I am sure that you would have tried to initialize it somewhere because it wouldn't make sense to use it otherwise, however if the initialization is behind a logic gate then the computer will throw this error. So:

public static void test() {
   int sum, m = 0;

   if(m == 0) sum = 15;

   System.out.println(sum + m);
}

This would be invalid code because the initialization of sum is behind a logic gate Even though you know that m equals 0 so that logic will always be true, the computer is not able to make that connection. Make sure that the variable is initialized outside of any logic gates. Here are some examples of acceptable initialization:

int sum = 0, m = 0;

int sum, m = 0;
sum = 0;

int sum, m = 0;
if(/*some conditions*/)
   sum = 10;
else
   sum = 15;
// this works because sum gets initialized one way or the other

A couple examples of not acceptable initialization:

int sum, m = 0;
if(/*some conditions*/)
   m = 10;
else
   sum = 15;

int sum, m = 0;
if(/*some conditions*/)
   sum = 10;
else
   m = 15;

Both of these leave sum in a position where it may not be initialized so both are invalid. It is important to note that the error would only occur on the use of sum meaning if it was never used after these then no error would occur.

Andrei

Level 41

4 September 2020, 14:01

Hi Guadalupe, thank you for the detailed answer! Let me see if I understand this correctly: If I declare

int sum, m = 0;
if(/*some conditions*/)
   m = 10;
else
   sum = 15;

And then I do not us the sum variable anywhere else, this declaration would be accepted. However, if somewhere, down the code line, I try to use the sum variable again, then this would mean that an error would be thrown at this point. Have I understood correctly? Thanks again for taking the time to provide such a detailed answer. Andrei.

Guadalupe Gagnon

Level 37 , Tampa, United States

4 September 2020, 14:21

Yes. The errors only occur when trying to use a variable that has not been declared, not in declaring them or initializing them. What that means is:

int sum;
System.out.println(sum);

Line 2 in this snippet would be the error, not line 1, because the code is attempting to use an uninitialized variable. In the code snippet that you just shared there is no error because "sum" is not used, however if you added an output line on line 6 (like the one on line 2 here), the same error would occur on that line of using an uninitialized variable. You can avoid this by always initializing variables with default values, such that dhanush suggested below, however as you become a more experienced programmer you will understand when you don't need to and when you do need to.

Andrei

Level 41

4 September 2020, 14:31

I see, ok! I think I understand better now, thank you!

dhanush

Level 30 , Chennai, India

26 August 2020, 11:35

No not like that you should initialize the variable with some value you can do in the same row like this

int sum=0, m=0;

Andrei

Level 41

27 August 2020, 09:16

HI Dhanush, thank you for your answer! I understand, however, I saw on another website a declaration like this int sum, m, n = 0; Is this type not possible at all? Thank you!

dhanush

Level 30 , Chennai, India

27 August 2020, 12:52

well may be if it is a member variable it will be assigned by itself if not it is in the local means it should however. Not possible i think so!

Andrei

Level 41

4 September 2020, 14:01

OK, I think I understand better now, thank you!