'string' does not name a type

[mnasiriqbal]

#ifndef ADD_H_
#define ADD_H_

#include <string.h>

int add(int, int);
string cat(int, int);

#endif /* ADD_H_ */

when i compile the code I get the following error
'string' does not name a type

i tried using string as well but get the same error. can anyone tell me what wrong I am doing here.

[Moschops]

#include <string>

using std::string;

int add(int, int);
string cat(int, int);

[mnasiriqbal]

thnx, it worked now with above modifications.