How is the code interpreted if no curly braces follow a while loop?

Question

I am new to programming, and can not understand how the following code is interpreted by the compiler. As you can notice in the code, the while loop does not have curly braces around the code that comes right after it. Can somebody please explain to me, step by step, how this loop works:

int num = 0;
while(++num < 6) 

    Console.WriteLine(++num);
    Console.WriteLine(num++);
    Console.WriteLine(++num);

Without braces the loop is only the first `Console.WriteLine` the other two happen after the loop. Indentation doesn't matter in C# except to make it more readable for humans. — juharr, Aug 26 '18 at 11:24
Debugger is the best friend to understand how the code works — Chetan, Aug 26 '18 at 11:31
I'm voting to close this question as off-topic because you could step through it with a debugger yourself and find out. — EJoshuaS - Stand with Ukraine, Aug 26 '18 at 14:27
Also, duplicate of [What is a debugger, and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — EJoshuaS - Stand with Ukraine, Aug 26 '18 at 14:29

score 4 · Accepted Answer · answered Aug 26 '18 at 11:52

A while loop without braces is the same as a while loop with braces surrounding the line immediately below it:

int num = 0;
while(++num < 6) 
{
    Console.WriteLine(++num);
}
Console.WriteLine(num++);
Console.WriteLine(++num);

First iteration:

while(1 < 6) // num is 1
{
    Console.WriteLine(2); // num is 2
}

Second iteration:

while(3 < 6) // num is 3
{
    Console.WriteLine(4); // num is 4
}

Third iteration:

while(5 < 6) // num is 5
{
    Console.WriteLine(6); // num is 6
}

On the fourth iteration, num becomes 7 and then gets checked by < 6, which evaluates to false. The while loop exits and the two lines below gets executed.

// num is 7
Console.WriteLine(7); // num is 8
Console.WriteLine(9); // num is 9

So it prints 2, 4, 6, 7, 9

score 0 · Answer 2 · answered Aug 26 '18 at 12:16

Since ommitting curly braces can quickly lead to unexpected behavior or hard to read code, it is good practice to always write them, even if not needed. Consider the following code (I have left out the indentation on purpose):

int i, j;
for (i=0;i<10;i++)
for (j=0;j<10;j++)
if (j > i)
continue;
foo(i, j);

Nobody will be able to read that, and even if you add the spaces, it's very error prone. Also, if you later need to add another line to the if () condition, you'll very likely forget to also add braces. (The example is very poor: foo(i,j) will only be called once and the loop will do nothing!)

Also beware of the following slightly modfied code from your question:

int num = 0;
while(++num < 6); // Careful: a semicolon ends the statement
Console.WriteLine(++num);

This will run the loop six times before even calling Console.WriteLine once, because the semicolon ends the statement.

Thank you!! I know its bad not using curly braces, im just playing with the code so i can understand how it all works, Thanks again — Gama47, Aug 27 '18 at 19:08

How is the code interpreted if no curly braces follow a while loop?

2 Answers2