What does a single semicolon in a for loop mean?

Question

I was following a tutorial for how to make an insertion sort and came across this line of code:

for(; j >= 0 && tempVar < insertionArray[j]; j--)

My question is, what does the single semicolon mean after the first bracket?

I know that a double semicolon in a for loop defines an infinite loop,

for(;;)

but what does a single one mean?

The same as [in other languages like C++ or C](https://stackoverflow.com/questions/16113125/two-semicolons-inside-a-for-loop-parentheses). — Uwe Keim, Apr 28 '19 at 11:06
It means one does not declare and assign counter `j` in the loop, but it should be done somewhere else before the loop. — CSDev, Apr 28 '19 at 11:06
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/for — chadnt, Apr 28 '19 at 11:08

score 1 · Answer 1 · answered Apr 28 '19 at 11:18

There are 3 parts to a for loop, each separated by semicolons:

      initialisation;   evaluation  ;  iteration  
for (   int i = 0   ; i < someValue ;     i++    )

If you have already initialized the variable that you want to evaluate and iterate through, you don't need to do it in the loop:

int i = 0;

for(; i < someValue ; i++ )

score 0 · Accepted Answer · answered Apr 28 '19 at 11:06

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The first part of a for loop is to declare and initialize the counter variable (j in this case). Since it was declared and initialized before the loop, we don't do it again.

answered Apr 28 '19 at 11:06

Albert

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score 0 · Answer 3 · edited Apr 30 '19 at 10:42

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It divides the line into different blocks.

The first part is one time statement, the second is the condition of the loop and the third is a operation to do after/before the loop's code.

edited Apr 30 '19 at 10:42

marc_s

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answered Apr 28 '19 at 11:07

Maor Tslakishvili

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score 0 · Answer 4 · answered Apr 28 '19 at 11:08

This just the initializer section The statements in the initializer section are executed only once, before entering the loop. The initializer section is either of the following:

The declaration and initialization of a local loop variable, which can't be accessed from outside the loop.

Zero or more statement expressions from the following list, separated by commas:

assignment statement

invocation of a method

prefix or postfix increment expression, such as ++i or i++

prefix or postfix decrement expression, such as --i or i--

creation of an object by using new keyword

await expression

What does a single semicolon in a for loop mean?

4 Answers4