Register Array position location

[Altera_Forum]

I define a register group as : 

reg[63:0] temp; Can I use a variable of "reg[6:0] a" to the temp as temp[a:0] ? when ""reg[6:0] a" is input port,it may work.But when the "a" is calculated in the design,i.e.it's not a ration,how the expression turns out ? thank u!