While loop to for loop issue

Question

I know it's a simple question but can someone help me figure out how to convert this while loop to a for loop. I keep getting an error trying to convert it

static string CountLines(string s)
{
    long count = 0;
    int start = 0;

    while ((start = s.IndexOf('\n', start)) != -1)
    {
        count++;
        start++;
    }
    return count.ToString();

}

This is the way I tried

for (int start = 0; start !=-1 ; start = s.IndexOf('\n', start)) {
   count++;
   start++;
}

You are basically counting occurrences of a character in a given string. Namely the `\n` character in your case. Your choice is one of many ways to do that. There are alternatives, some using LINQ, which can be clearer. See https://stackoverflow.com/questions/10391481/number-of-occurrences-of-a-character-in-a-string — DodgyCodeException, May 25 '18 at 16:32
Why are you trying to convert this to a for loop? It is so much better code as a while than as a for loop... — Chris, May 25 '18 at 16:32
http://rextester.com/MXHL85276 For loop counts correctly where while loop is out by one but seems to work. — Chris Nevill, May 25 '18 at 16:34
Also [How to count lines in a string?](https://stackoverflow.com/q/11189331/719186) — LarsTech, May 25 '18 at 16:35
`for` vs `while` has nothing to do with parallel vs sequential execution. You would need to change the algorithm to do it in parallel, such as just simply checking each character because as you have it now, each subsequent iteration depends on the result of the previous iteration (as you pass the new value of start into `IndexOf`) — clcto, May 25 '18 at 18:32

itsme86 · Answer 1 · 2018-05-25T16:27:50.067

2

for loops have the following structure:

for (<initialization>; <condition to keep running>; <iterative statements>)
    <loop body>

So, first step, you want to move the condition from your while loop statement into that middle section of the for loop statement.

for (something; (start = s.IndexOf('\n', start)) != -1; something;)

Now, we can introduce the initialization (int start = 0) to the first part and the iterative statement (start++) to the last part:

for (int start = 0; (start = s.IndexOf('\n', start)) != -1; start++)
{
    count++;
}

And there you have it.

edited May 25 '18 at 16:27

answered May 25 '18 at 16:25

itsme86

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I think the whole point of moving to for was to get rid of the assignment in the conditional. – clcto May 25 '18 at 16:26
1

@clcto And how did you come to that conclusion? I don't see it mentioned anywhere by OP. – itsme86 May 25 '18 at 16:27
Because he moved it out of the conditional and it is a common style guideline to not do that. – clcto May 25 '18 at 16:27

While loop to for loop issue

1 Answers1