clear
set obs 10
set seed 1357911
gen x = int(130*uniform())
replace x=100 in 3
replace x=100 in 8
replace x=100 in 10
list x

sort x
gen n = _n
list

gen is100=(x==100)
gen cum_is100 = sum(is100)

gen num_first100 = n if cum_is100==1
*-or
list n if cum_is100==1

谢谢连老师