Compiler says a string doesn't name a type when it does

[pepstein]

This is a .h file for a slightly larger program where the program counts the number of uses of the words in a text file. The compiler keeps telling me that the 'string' doesn't name a type but it does have a type named word?

#ifndef CONCORDANCE_H
#define CONCORDANCE_H

#include <iostream>
#include <string>

struct Entry {
	string word;
	int frequency;
};

void add(Entry concordance[], int &size, const string word);
int lookup(const Entry concordance[], int size, const string word);

#endif 

the errors are:
lines 8 and 12 and 13: error: 'string' doesn't name a type
also, lines 12 and 13: error: ISO c++ forbids declaration of 'word' with no type [-fpermissive]

any help would be appreciated, thanks.

[Peter87]

All standard classes and functions are inside the std namespace so write std::string.

[pepstein]

thanks, that fixed it