Sum string hours and minutes sample

hi, thank you for the script, I m looking to Concatenate two variable do you know how may I do it ?

for exemple :
x1 = if ((o1-c1)/c1)*100 > input
1

x2 = if ((o2-c2)/c2)*100 > input
2

plot(x1 & x2)

the result should be 12 or 1 or 2 or n/a