I want to split after 20 characters in a given string and i want to place in another string

Question

Hi
In my applcation for  example there are  160 characters or more .... i want to split after 20 characters in next line
if hi karthik is there i want to break after the completion of word.

string str=some 160 characters or more

// and  i want to break after 20 characters and iwant to  place in another string

plz help me how to split...