What's the range of this for loop? [duplicate] - for-loop

Question

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for loop missing initialization
(6 answers)
Closed 3 years ago.
I'm new to CS, and found this code online. What does this blank between two semicolons indicate? What's the range of this for loop? Thanks.
for (int i = 0, temp; ; i++)

Answer 1

This is the typical structure of a for loop:
for(initialization; condition ; increment/decrement)
{
statement(s);
}
but yours is as follows:
for(initialization; ; increment)
{
statement(s);
}
As you can see the condition part is removed which is completely valid, but this just means that the loop will run infinitely.
Typically in cases like this, some logic inside the loop block will be responsible to break out of the loop given some condition is met.

Answer 2

If you look at the reference for for at learn.microsoft.com you can see the following example.
The following example defines the infinite for loop:
for ( ; ; )
{
// Body of the loop.
}
The infinity comes from the "the condition section" being empty. Again from the reference:
The condition section, if present, must be a boolean expression. That expression is evaluated before every loop iteration. If the condition section is not present or the boolean expression evaluates to true, the next loop iteration is executed; otherwise, the loop is exited.
Here's a bad clock implemented via a never-ending loop to show the difference between how i and temp change as the loop progresses.
public async static Task Main(string[] args)
{
var start = DateTime.Now;
for (int i = 0, temp; ; i++)
{
// 'i' is a) initalised and b) incremented after each
// 'temp' is a) *un*initialised and b) doesn't automatically change
temp = 666;
Console.WriteLine($"It's now {DateTime.Now.TimeOfDay} and this is about {i} seconds after {start.TimeOfDay}. 'temp' is {temp}");
await Task.Delay(TimeSpan.FromSeconds(1));
}
}
Output:
It's now 09:07:02.9269857 and this is about 0 seconds after 09:07:02.9246017. 'temp' is 666
It's now 09:07:04.0195240 and this is about 1 seconds after 09:07:02.9246017. 'temp' is 666
It's now 09:07:05.0223953 and this is about 2 seconds after 09:07:02.9246017. 'temp' is 666
It's now 09:07:06.0379706 and this is about 3 seconds after 09:07:02.9246017. 'temp' is 666
It's now 09:07:07.0482980 and this is about 4 seconds after 09:07:02.9246017. 'temp' is 666

Answer 3

See the docs for for:
The for statement defines initializer, condition, and iterator sections:
for (initializer; condition; iterator)
body
All three sections are optional.
Also, from the same source:
If the condition section is not present or the boolean expression evaluates to true, the next loop iteration is executed; otherwise, the loop is exited.
(emphasis mine)