As long as you only need to test a few globals it should be fine, but if you plan on testing a lot then i wouldnt use it either.
But a way you can do it, is by adding a local variable or global, whatever suits you.
Lets call it:
Then you add:
If G1 < G2 Set lowest_value_found = G1.value
After that you test the next one against than value.. so:
If Lowest_value_found > G3 then Set lowest_value_found = G3.value
and then you continue.
I dont think there is a way to loop through Global variables, so using this method is really bad if you have to test like 1000s, as you would have to do a lot of tests. Then you would be better off, using an array as already suggested. If you dont like arrays you can do it with a list as well.