How does “()” convert statements into expressions in C++? [duplicate]
This question already has an answer here: Are compound statements (blocks) surrounded by parens expressions in ANSI C? 2 answers I have the following code: int main() { int i=0; int j=({int k=3;++i;})+1; // this line return 0; } It compiles and runs. If I remove the () from "this line", then it doesn't compile. I'm just curious what syntax rule is being applied here. The {} contains 2 statements, and the last statement indicates the "return" value of this code block. Then why does it need an extra () pair to make this return value usable? That's a statement expression, and it's a GCC-specific extension. From the linked reference: A compound statement enclosed in parentheses may appear as an expression in GNU C. This allows you to use loops, switches, and local variables within an expression. A compound statement is a curly-brace enclosed blo...