These functions, to some, may seem trivial, but many people have queried in the forums on this topic numerous times.

The functions are templated, so that it can accommodate any data-type that the user wishes to use (For example, the same function can be used for converting variables of type long , int , double etc into strings, and vice-versa).

The first function, Fn I ( convertToString ), is capable of converting a variable of any data-type into a string.
Sample Function Call:

string MyInt = convertToString<int>(10);

The second function, Fn II ( convertFromString ), can convert a string into a variable of any data-type.
Sample Function Call:

int MyNumber = convertFromString<int>("45");

*Note*: You will have to include the header files - <sstream> and <string.h> for the code to work...

Hope this snippet helps....

     This Function (Fn I) converts a variable of
     data-type DataType into a string
template <typename DataType>
string convertToString(DataType MyValue)
     // Creates a Output String Stream to hold
     // the variable passed (MyValue)
     ostringstream OutStream;
     // Enter the variable into the stream
     OutStream << MyValue;
     // Return the stream as an array of
     // characters(string)
     return (OutStream.str());

     This Function (Fn II) converts a string into
     a variable of data-type DataType
template <typename DataType>
DataType convertFromString(string MyString)
     // Stores the return value
     DataType retValue;
     // Creates an Input String Stream to extract
     // the contents of the string
     istringstream InStream(MyString);
     // Read contents of String and store in retValue
     InStream >> retValue;
     // Return the value in the desired DataType
     return retValue;

And it's well commented and it addresses a common beginner's problem :)
Though I'm not so sure about the <string.h> you've to include, it has to be <string>, string.h contains several functions which operate on c-strings ...

Nice snippet!