Change c++17 to c++20. Fixed formatting on assignment from double.

compile

@@ -5,7 +5,7 @@ do
    filename="${file%.*}"
    list="$list $filename.o"
    echo -n "Compiling $filename..."
-   g++ -g -c $file -std=c++17 &
+   g++ -g -c $file -std=c++20 &
    if [ $? = '0' ]
    then
     echo "OK"