Brace Usage

All if, while and do while statements must either have braces or be on a single line. It ensures that when someone adds a line of code later there are already braces and they don’t forget. It provides a more consistent look and this doesn’t affect execution speed.

Good

if (condition) {
  return 0;
}

Good

if (condition) ++i;

To illustrate what can go wrong consider an example shown below which does not use braces.

Bad

if (condition)
  ++i;

The code can be later modified by adding more statements in the if condition but forgetting to put the braces.

Bad

if (condition)
  ++j;
  ++i; // misleading. Seems like it's executed when the conditions is true

By mistake, the code is now executing ++i every time, even when the condition is false. This is because the indentation does not any effect on the scope of statements that belong to the if, only braces have. As a result, the above code is equivalent to:

Good

if (condition) {
  ++j;
}
++i;

where it is clear that ++i is executed all the time.