Ravi, you have been given a hard time from posting this question - because there are so many ways to represent numbers such questions have to be put very carefully.

Do you actually want an equivalent function to C's atoi?:

http://man.he.net/man3/atoi

Which is equivalent to (int)strtol( s, (char**)NULL, 10) - i.e. also see:

http://man.he.net/man3/strtol