'For' loop pre and post empty statements - go

Question

What does it mean in Go that the pre and post statements of a for loop are empty, like in the following example?
sum := 1
for ; sum < 10; {
sum += sum
}
fmt.Println(sum)

Answer 1

Remember that a for loop is the same as a while loop.
Your code can be rewritten in other languages as
sum := 1
while(sum < 10) {
sum += sum
}
fmt.Println(sum)
In a for loop, there are 3 parts.
for(initial statement ; condition ; end statement usually iterate)
This is equivalent to
initial statement
while(condition) {
Stuff here
End iteration statement
}
The reason your loop can be written withiut the pre and post statements is because you've specified them in other parts of the code.

Answer 2

It behaves like a while in other languages. You don't need the two semicolons:
sum := 1
for sum < 10 {
sum += sum
}
fmt.Println(sum)

Answer 3

A for loop has three elements: initialization statement, condition check, and variable change.
for <initialization statement>; <condition check>; <variable change>{
<actual body>
}
The initialization statement is executed only once when the loop starts. Based on the name, it initializes something (in a lot of cases a variable you iterate through). If it is omitted, then it does nothing
The condition check verifies whether the condition evaluates to true. If it is not, the loop stops. If it is omitted, then it is always true.
The variable change is modifying variables during each iteration of the loop. Most of the time, the iterated variable is increased/decreased, but you can do whatever you want. If it is omitted, it does nothing
After this explanation, you can see that this loop does nothing during your initialization and post condition phase.
You also do not need to use semicolons here. This will be enough.
sum := 1
for sum < 10 {
sum += sum
}
You can even write a loop like this: for {} which will never stop executing, or do something like a while loop:
t := 10
for t > 0{
t--
}
Note that inside your initialization, condition, and change phase you can use many expressions (not just one). So with a simple while loop you can do something like:
for f1, f2, n := 1, 1, 10; n > 0; f1, f2, n = f2, f1 + f2, n - 1{
fmt.Println(f1)
}
which creates Fibonacci numbers—see Go Playground. Showing this not because this is the best way to write it, but rather because it is possible.