Tcl and OTcl Tutorial For NS2 variables and arrays Variables and arrays Defining a variable in Tcl is very simple: set var1 1 set var2 "Tcl Variable 2" The variables can be referenced by prefixing the variable name with a $. For example to print the above variables, we can use puts "var1=$var1, var2=$var2" Any situation in which you require that the value of the variable be used is one in which the $ prefix should be added to the variable name. In some situations, it is necessary to use the variable name directly. For example incr var1 can be used to increment var1. I guess you can think of it as the difference between call-by-reference and call-by-value: in the former case you use the variable name on its own, while in the latter you prefix it with a $. An alternative is to assign the results of a function to a variable. This can be done as follows: set var3 [expr 5*10] This sets the variable var3 to the result of calling the expr function with the parameter 5*1...