I have a set of variables labelled b_01, b_02, b_03.....b_11, b_12, ....b_20 and similarly another set of variables labelled bord_01....bord_20

I want to create a new variable using these two sets and I used the following code:
Code:
gen child1 = .
forval i = 01(1)20{
replace child1 = b2_`i' if bord_`i' == 1
}

But I keep getting the following error message

Code:
b2_1 ambiguous abbreviation
r(111);
I am not sure how to circumvent this to make the code recognize that b2_01 is different from b2_11.