Why does C allow leaving out braces around blocks? [closed] - c

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Most of us have probably encountered the bug of when you add another statement inside an 'if' and notice that it prints regardless of the condition of the branch, only to find out sooner or later in frustration that the braces around the 'if' condition was missing.
Example:
if (condition) {
statement;
}
Compared to:
if (condition)
statement;
Please note that I wouldn't want a discussion on what coding standard is better, as we all have our opinion about that and it's very much dependent on context. Instead, I would be interested in the advantages from a programming language point of view and from these advantages, why it was decided not to be strictly enforced. Does it make for a simpler grammar? Compiler implementation?
What is the advantage of leaving it optional, rather than strictly enforcing it? What does the standard say about it?

Answer 1

The C Standard says that a if (expression) must be followed by a statement. It does not require the statement to be a compound statement.
In the "Spirit of C" (see C Rationale document), one of the phrase is:
Trust the programmer.
MISRA-C on the other hand has a required rule for if and loops that the statement has to be a compound statement.
Some coding styles allow a single statement for if only if the statement is put in the same line as the if. For example:
if (condition) statement;
Note that C and C++ are not only the languages to have the {} be optional in if. For example in Java it is also optional, but in Perl it is required.

Answer 2

Because:
that would be excessive meddling — the programmer chooses coding style, not the language;
it would further complicate the grammar; easier and more robust to just say that an if (condition) is followed by a statement and let the recursion handle everything.
Personally I find the distrust of this construct to be largely without merit for any vaguely competent programmer; I've not once encountered this "bug" where I've forgotten how to write C++ just because I chose to omit a brace pair. If you come across it, I suggest you treat it as a cue to pay more attention to what you're doing, rather than masking it with "tricks" and "style guides".

Answer 3

Sometimes, not having to write the braces makes the code more readable imho:
if (x < 0) throw std::invalid_argument("meh");
if (a != b) return 0;
if (i == k) continue;
In theory, you could design a programming language to require braces except for control flow statements, but this safety would probably be outweighed by the additional language complexity.

Answer 4

C/C++ also doesn't mandate strict adherence to K&R style. For people who prefer Allman style, the extra braces are completely unnecessary:
if (condition)
statement;
if (condition)
{
statement;
statement;
}
With the introduction of lambdas and braced initialization, we are seeing an increasing number of braces in our code and I think Allman style actually manages it better.

Answer 5

You misunderstand it slightly. The braces are neither optional nor compulsory. There was no decision about whether to allow them or to enforce them at all. The braces are not part of the if statement (or any similar construct). They belong to the statement that follows the condition. Simple statements will not have them but compound statements will (by definition, a compound statement is a list of statements enclosed in braces).
This situation and how the compiler handles it comes directly from this syntax definition (which is, actually, nothing C-specific, most other languages of the era that I can think of, Algol, Pascal, whatever, even if they used keywords instead of braces, do the very same). Basically, any language that has no specific ending keywords (like if and end if or if and fi) have to handle it this way.
When you do include the braces around a single statement in an if or any other similar construct, you don't use an optional form of if allowing braces. You just happen to provide it with a compound statement (hence, enclosed in braces) consisting only of a single statement inside, and this is perfectly legal. But it's the same for the compiler, it doesn't handle it any different.
Actually, but this is a question of taste, of course, many programmers prefer to omit them because it reduces clutter.

Answer 6

A scope is merely a compound statement. It can be placed anywhere:
void foo() {
int a = 0;
a = 1; // this is a simple statement.
{ // this is inside a scope. It is a compound statement. Note that I don't need an if.
a = 2;
a++;
}
return a;
}
Being able to put any statement (compound or not) after an if, while or other constructs makes the syntax much simpler to implement.

Answer 7

C was created in a time when computers had 40×25 character graphics.
If you want to have indentation of the condition block/statement
you save one (opening brace on the same line) or two lines (opening brace on the following line):
if (condition)
statement;
if (condition) {
statement;
}
if (condition)
{
statement;
}
So saving a line was important. It allowed to show more source code in one screen.