I'm learning operations with " + ", " - " and " * ", addition and subtraction works well, but multiplication gives me only additions, link for the code:
http://www.edaplayground.com/x/NvT
I checked the code, can't understand what's going on. I gave enough space (bits) the result variable.
BTW, It's a code intended for fixed-point operations including fractional numbers, but everything is calculated as integers.
Your select signal is only on 1bit.
Then when you set select = 2 it assigns the lower bit of 2(2'b10) i.e. 0.
You should change select declaration by :
input [1:0] select; // In the module
reg [1:0] select; // In the testbench
To avoid such errors I would advise you to use the complete notation of values:
x'tnnn...nnn
where x is the width of the signal, t is the type (d for decimal, h for hexa, b for binary,...) and nnn...nnn the value in the type specified.
For example for the decimal value 2 you will have several notations that will make sense in certain situations:
2'd2 //2 bits decimal
2'h2 //2 bits hexadecimal
2'b10//2 bits binary
For more informations about these notations you can read this pdf.