Integer problem....

It depends of how you write your testbench.

1. You can write a counter in your testbench in VHDL which feeds the input of "adder_integer"

2. You can write a macro macro_adder_integer.do (simple text file) which looks like :

#  increase "astring" from 0 to 15
for {set inc 0} {$inc <= 15} {incr inc} {
  #  generate stimuli
   force -freeze sim:/adder_integer/astring 0 10#$inc#
  #  simulate
   run 20 ns;#  arbitrary value since you don't have clock in your design (typically 50Mhz)
}

And then in modelsim prompt, type do macro_adder_integer.do

ModelSim Macros are in TCL langage

3. type

force -freeze sim:/adder_integer/astring 0 10#0#

run 20 ns

force -freeze sim:/adder_integer/astring 0 10#1#

run 20 ns

...

force -freeze sim:/adder_integer/astring 0 10#15#

run 20 ns

:-D