how to find string contain.

Dear all,

i want to find some char from a given string like below example

vtext = PM-BGM12_AC :

if vtext contain '_AC' then i have to assinge btext = ' Air Conditioner'.

if vtext = PM-BGM12_BPI contain '_BPI',

then i have to assign btext = ' Building & Permanent Improvement '

i m consfuse what to user ca , co, cs, cp.

*********point is assured *********