Declarations/definitions as statements in C and C++

Question

I was confused when this wouldn\'t compile in C:

int main()
{
    for (int i = 0; i < 4; ++i)
        int a = 5; // A dependent statement may not be declarati         


        

Answer 1

C++ allowed that the "substatement" of an iteration statement was implicitly a compound statement ([stmt.iter])

If the substatement in an iteration-statement is a single statement and not a compound-statement, it is as if it was rewritten to be a compound-statement containing the original statement. Example:

while (--x >= 0)
   int i;

can be equivalently rewritten as

while (--x >= 0) {
   int i;
}

the C standard does not have this language.

Additionally, the definition of a statement changed in C++ to include a declaration statement, so even if the above change wasn't made, it would still be legal.

---

The reason that adding braces makes it work is because your declaration now becomes a compound-statement which can include declarations.

You are allowed to have an identifier in a loop body without braces, so you can do this instead:

int a = 5;
for (int i = 0; i < 4; ++i)
    a;