You want install g++ package?
The command is sudo apt-get install g++

be clear on what u said...cause ./configure will tell u what u missing, on the other hand, just copy the whole thing after u input ./configure

ok, u extract the file u dl-ed into ur home folder, folder name should be the same as the file u just extracted.
now use console, type in "cd ./[the folder name]", once ur in, use "./configure && make && sudo make install" just copy without the quote. after u done it, u need to set ur system to use this gcc instead of the 1 comes with ubuntu...if u did not have gcc in ubuntu, install thru package manager, dont bother to compile cz u seems to be very fresh in linux...without gcc, u cant make...

What's your output for echo $PATH?

You don't have to download the gcc source code from the gcc site. You can install the compiler using the apt-get command. Run the following commands to install the necessary files to compile programs:

sudo apt-get install build-essential

This should install the gcc along with g++ on your machine.