make file is throwing below two error - c++

Question

Hello i have created four file fn.cpp header.h,main.cpp and makefile
I am getting two error plz help to fix it.
fn.cpp:1 error: string was not declared in this scope? why?
fn.cpp:2 error :expected ',' or ';' before '{' token?
header.h:
#include<iostream>
#include<string.h>
#include<stdio.h>
using namespace std;
int fn(string);
main.cpp:
#include "header.h"
string s= " hello world";
int main()
{
fn(s):
}
fn.cpp:
int fn(string ss)
{
printf("%s",ss);
}
makefile:
all:hello
hello:main.o fn.o
tab g++ main.o fn.o-o hello
main.o:main.cpp
tab g++ -c main.cpp
fn.o:fn.cpp
tab g++ -c fn.cpp

Answer 1

The std::string class is defined in the <string> header. Include that instead of the C library's <string.h> header.
Also, you need to include "header.h" from both source files.
Finally, you can't pass a string object directly to printf; that's a C function which knows nothing of C++ classes. Either use C++ I/O:
std::cout << ss;
or faff around with C-style strings:
printf("%s", ss.c_str());

Answer 2

many small "out of c++ style" problems :)
use header #include <string> and avoid printf if you can, better use cout
c++ lovers would like this a little bit more:
fn.h
#include<string>
void fn(const std::string&);
fn.cpp
#include <stdio.h>
#include "fn.h"
void fn(const std::string& ss)
{
printf(ss.c_str());
}
hello.cpp
#include "fn.h"
std::string s = " hello world";
int main()
{
fn(s);
}
Makefile
all: hello
hello: hello.cpp fn.o