Why does this work?

[Ktchnking]

My answer for the challenge in 67- Checking Characters Part 2 was a bit different than the answer provided after the challenge and I want to find out why as I was not sure of my answer even though it appears to work fine.

The solution offered after the challenge seems to disagree with what I thought would happen.

I know there are multiple ways to do things but I have no prior experience and want to know why it works.

Thank you!

bool UBullCowCartridge::IsIsogram(FString Word) const

{

// for(int32 Index = 0, Comparison = Index + 1; Comparison < Word.Len(); Comparison++)

// {

//     for(int32 Comparison = Index + 1; Comparison < Word.Len(); Comparison++)

//     {

//         if (Word[Index] == Word[Comparison])

//         {

//             return false;

//         }

//     }

// }    

for(int32 Index = 0, Comparison = Index + 1; Comparison < Word.Len(); Comparison++)

{

    for(Index = 1; Comparison < Word.Len(); Comparison++)

    {

        if (Word[Index] == Word[Comparison])

        {

            return false;

        }

    }

}

return true;

}

[Ktchnking]

It would seem that with my solution any word other than a correct guess output “There are no repeated letters.”

So- it does not work as I stated in the post above.

If I understand what this function is doing (checking the remaining characters past 1 for a match,)

Why would I end up with the PrintLine from the !ISISogram if statement.

If none of the characters in the rest of the string are the same as the character in 1 wouldnt the game read it as a wrong answer and deduct a life instead?

Here is the code incase it is asked for

bool UBullCowCartridge::IsIsogram(FString Word) const

{

// for (int32 Index = 0, Comparison = Index + 1; Comparison < Word.Len(); Comparison++)

// {

//     for(int32 Comparison = Index + 1; Comparison < Word.Len(); Comparison++)

//     {

//         if (Word[Index] == Word[Comparison])

//         {

//             return false;

//         }

//     }

// }    

for (int32 Index = 0, Comparison = Index + 1; Comparison < Word.Len(); Comparison++)

{

    for(Index = 1; Comparison < Word.Len(); Comparison++)

    {

        if (Word[Index] == Word[Comparison])

        {

            return false;

        }

    }

}

return true;

}

[DanM]

Could you describe what your loop does line by line each iteration for the word “plan”?

[Ktchnking]

I am sorry but I do not understand your question. I have not used the word plan.

[DanM]

I’m asking for you to state what is happening in your loop if the word “plan” is passed into it. It doesn’t matter what word, I just want you to explain what your loop is doing so you understand why it’s wrong.

What happens line by line?

[Ktchnking]

I understand now. Thank you.

This is what I think:

for (int32 Index = 0, Comparison = Index + 1; Comparison < Word.Len(); Comparison++)

loop (Index is the first character in the string, Comparison is the next character; comparison will not go past the last character in the string; Comparison will look at the next character each loop)

for(Index = 1; Comparison < Word.Len(); Comparison++)

Loop (Index starts at the second character; Comparison still wont go past the last character; Comparison will look at the next character each loop)

    if (Word[Index] == Word[Comparison])

if (the character in the word is the same as the character in the comparison return the Boolean as false

[DanM]

I forgot to add “each iteration” to the last reply. For example with the following code

for (int32 Index = 0; Index < 3; ++Index)
{
    PrintLine(TEXT("%i"), Index);
}

I’m asking you to do something like this

• Initialise Index to 0
• Check if Index is < 3, it is so it enters the loop
• PrintLine with the value of Index (0)
• Increment Index by 1
• Is Index (1) < 3, it is so the loop continues
• PrintLine with … etc.

But for your own code.

[Ktchnking]

Ok.
for (int32 Index = 0, Comparison = Index + 1; Comparison < Word.Len();Comparison++)

• initialize index to 0

• initialize comparison to index plus 1

• check comparison is less than string length

• do again until comparison reaches the end of the string

  for(Index = 1; Comparison < Word.Len(); Comparison++)

• initialize index to 1

• check comparison is less than the string length

• do again until comparison reaches the end of the string

•     if (Word[Index] == Word[Comparison])
  

if the index value and the comparison value are the same character return false

        return false;

During the challenge my initial thought was I would need to duplicate the code with the index value counting up until it reached the end of the string.

The solution you gave using the Comparison = Index + 1 makes since as with one line of code the loop does that. If I am understanding correctly.

[DanM]

@Ktchnking

do again until comparison reaches the end of the string

It’s unclear by what you mean but that doesn’t happen all on the first iteration.

@Ktchnking

• initialize index to 1

technically an assignment not initialisation.

---

What your code does with the word “tan”

• Initialise Index to 0, Comparison to 1.
• If Comparison (1) is < 3 enter loop body
• Assign Index to 1
• is Comparison (1) is < 3 enter loop body
• Is Word[1] == Word[1] the same character, yes so return false.

Which is incorrect as “tan” is an isogram and also will always return false no matter what you enter.

If you remove Index = 1 from the second loop it will still be incorrect because it does the following. Changing the word to “abb” to illustrate the issue with it now

• Initialise Index to 0, Comparison to 1.
• If Comparison (1) is < 3 enter loop body
• is Comparison (1) is < 3 enter inner loop
• Is Word[0] == Word[1] the same character (a == b), no
• Increment Comparison by 1 (2)
• Is Comparison < 3, enter loop body
• is Word[0] == [2] (t == n), no
• Increment Comparison (3)
• Is Comparison < 3, no exit inner loop
• Is Comparison < 3, no exit loop and return true.

Which is incorrect as “abb” is not an isogram.

---

What the course does with the word “abb”

• Initialise Index to 0
• if Index < 3, enter loop body
• Initialise Comparison to Index + 1 (1)
• If Comparison < 3, enter loop body
• Word[0] == Word[1] (a == b)
• Increment Comparison (2)
• If Comparison < 3, enter loop body
• Word[0] == Word[2] (a == b)
• if Comparison < 3, false so the loop ends

Now here’s the crucial part

• Comparison goes out of scope
• Index gets incremented by 1
• If Index < 3, enter loop body
• Initialise Comparison to Index + 1 (2)
• 2 < 3
• Word[1] == Word[2] (b == b) so return false.

[Ktchnking]

Thank you for your patience, I see it see it now.