When can I omit curly braces in C?

Question

I\'m almost certain this has been asked before, but I can\'t find it being answered anywhere.

When can I omit curly braces in C? I\'ve seen brace-less return

Answer 1

The following seems a little tricky:

if (...)

        printf("I'm conditional\n");

I guess the C preprocessor takes care of empty lines, so this statement is fine. Very bad practice of course.

Answer 2

Anytime there is a block with more than one line (counting lines as a single statement with a ; )

Examples:

for (i = 0; i < j; i++ ) 
   foo(i);

while (1) 
   foo();

if( bool )
   foo();

void cheese()
   printf("CHEESE");

Everything after the ; in the above lines does not count as 'inside' the block as if there were { }.

Answer 3

If in doubt, use braces. They don't "cost" any extra [unless you absolutely use them incorrectly].

A fairly basic rule is "if you have more than one semicolon at the same indentation, you should have braces". It's not entirely that simple, but as a "one sentence with no ifs, buts or other complications" it will have to do.

And yes, Java being based on C-syntax has the same fundamental rules - there are possibly some weirdness where Java is different from C or C++, but that's unusual/strange things, not something you'd normally hit when writing typical code [I haven't done much java, so I can't say I've found any of them, but I'm pretty sure there are SOME differences - they are different languages, after all].

Answer 4

You can omit them when there's a single statement you're executing:

for(...)
 printf("brackets can be omited here");

if(...)
 printf("brackets can be omited here");
else
 printf("brackets can be omited here too");

etc.. You can always add them in, it never hurts and help to clarify the scope, but you're pretty safe. The only "catch" I can think of is if you attempt to make a declaration in that scope (which is useless by the way):

if(...)
  int a = 5;

This will cause an error, but that's because you can perform a single statement without curly brackets, not a declaration. Important distinction.

Technically speaking, you can even do more than one operation without brackets if they're concatenated with the , operator... not that I advice doing it, just worthy of note:

if(...)
    value++, printf("updated value with brackets");

And to your edit, you can see in the java specification that the rules are the same. I linked specifically to the if section, but you can see after the if it's expected a statement, thus you can skip the curly brackets.

Answer 5

The only places you can omit brackets are for the bodies of if-else, for, while, or do-while statements if the body consists of a single statement:

if (cond)
  do_something();

for (;;)
  do_something();

while(condition)
  do_something();

do 
  do_something();
while(condition);

However, note that each of the above examples counts as single statement according to the grammar; that means you can write something like

if (cond1)
  if (cond2)
    do_something();

This is perfectly legal; if (cond2) do_something(); reduces to a single statement. So, for that matter, does if (cond1) if (cond2) do_something();, so you could descend further into madness with something like

for (i=0; i < N; i++)
  if (cond1)
    if (cond2)
      while (cond3)
        for (j=0; j < M; j++)
          do_something(); 

Don't do that.

Answer 6

An example:

int a[2][2] = {{1, 2}, {3, 4}};

you can use the valid equivalent form:

int a[2][2] = {1, 2, 3, 4};

Some verbose compilers may warn, but it is valid.

Note that for the if statement (same for the while, the for statement, ...) the {} are not omitted. They are just not requested. The if statement has this syntax:

if (expression) statement

If you want a multiple statement instead of a single statement you can use a compound statement which is surrounded {}.