how to convert a fin.getline() char to integer?

Urgent......thank you so much...

Code:

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fin.getline(bufferVariable);
atoi(bufferVariable);
cout<<bufferVariable+1;
//think this is how you do it...but i know for sure it's the atoi() function

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i have add this to the program but there is error saying :" undeclared identifier".....

do i have to include any header file?
i have included <string.h> and <iostream.h>.

is that enough?
thank you !!!

>do i have to include any header file?
#include <cstdlib>
or
#include <stdlib.h> // For older compilers

-Prelude

sorry......that should be <fstream.h>

thank you so much....