HDLBits-Replication operator

{num{vector}}

Build a circuit that sign-extends an 8-bit number to 32 bits. This requires a concatenation of 24 copies of the sign bit(i.e., replicate bit[7] 24 times) followed by the 8-bit number itself. 

module top_module(
    input [7:0] in,
    output [31:0] out
    );

    assign out = {{24{in[7]}},in};
    //Error: assign out = {24{in[7]},in};

endmodule