Weird initialization in C

I have this piece of code and i don't know how it works

#include <stdio.h>

int main(void)
{
    int numero = ({const int i = 10; i+10;});

    printf("%d\n", numero); // Prints 20

    return 0;
}

Why if i delete the second part (i+10;), the compiler gets an error? Why are the br开发者_如何学JAVAackets necessary?

Thank you ^^!

It's a GCC statement expression. It executes the statements in it, and returns the value evaluated in the last statement. Thus numero is initialized to 20. If you delete the second part, there is no expression as the last statement, so it can't get a value from the statement expression.

The braces are necessary to disambiguate it from ordinary C parenthesized expressions.