It creates a compound literal [1] of type array of int, and initializes the specified array positions using designated initializers [2] with the results of calls to puts().

Using designated initializers without the = symbol is an obsolete extension.

[1] https://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html [2] https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html