Converting specific characters in a string

[Bob Lomax]

Here's a program description:
1)user enters a string: "Java Rules"
2)then enters a string containing
characters to be converted: "ae s" (characters in this case are 'a' 'e' '<space>' and 's')
3)user then enters an output character that the characters to be converted will be converted to:"$"
therefore the string "Java Rules" will become "J$v$$Rul$$"
can anyone suggest an efficient algorithm to deal with this problem?

[Cindy Glass]

This is in Intermediate. Please do not cross post.