must be nonstatic member function error

[JWP321]

Hi, when I compile my code for proj07.string.cpp, i receive the following errors:

proj07.string.cpp:31: error: 'String& operator=(const String&)' must be a nonstatic member function
proj07.string.cpp:42: error: 'String& operator+=(const String&)' must take exactly two arguments

I'm not sure how to overcome either error, any suggestions?
Note: I'm not allowed to change the header file, so any editing must be done on proj07.string.cpp

*********************************************************************************
//proj07.string.h

#ifndef STRING_
#define STRING_

using namespace std;

#include <iostream>

class String
{
private:

// Capacity of a string
//
static const unsigned int MAX = 64;

char Mem[MAX]; // Memory to hold characters in string
unsigned Len; // Number of characters in string

public:

// Construct empty string
//
String() { Len = 0; }

// Reset string to empty
//
void reset() { Len = 0; }

// Return status information
//
bool empty() const { return Len == 0; }
bool full() const { return Len == MAX; }

unsigned length() const { return Len; }
unsigned maximum() const { return MAX; }

// Return reference to element I
//
char& operator[]( unsigned I ) { return Mem[I]; }

// Return constant reference to element I
//
const char& operator[]( unsigned I ) const { return Mem[I]; }

// Construct string by copying existing string
//
String( const String& );
// Construct string by copying array of characters
//
String( const char [] );

// Copy string to the current string
//
String& operator=( const String& );

// Append string to the current string
//
String& operator+=( const String& );
};

// Return string which is the concatenation of two strings
//
String operator+( const String&, const String& );

// Compare two strings
//

bool operator==( const String&, const String& );
bool operator< ( const String&, const String& );

// Output string to stream
//
ostream& operator<<( ostream&, const String& );

// Input string from stream
//
istream& operator>>( istream&, String& );

#endif

**************************************************************************
//proj07.string.cpp

#include <iomanip>
#include <iostream>
#include "project07.string.h"
#include <string.h>

using namespace std;


String::String( const String& Copy)
{
int i;
Len = Copy.length();
for (i = 0; i <= Copy.length(); i++)
{
Mem[i] = Copy.Mem[i];
}
Mem[i] = NULL;
}

String::String( const char Array[])
{
int i;
for (i = 0; i < strlen(Array); i++)
{
Mem[i] = Array[i];
}
Len = i;
}

String::String& operator=( const String& Copy)
{
int i;
Len = Copy.length();
for (i = 0; i < Copy.length(); i++)
{
Mem[i] = Copy[i];
}
Mem[i] = '\0';
}

String::String& operator+=( const String& Copy)
{
int i;
for (i = 0; i < Copy.length(); i++)
{
Mem[Len] = Copy[i];
Len++;
}
}
String operator+(const String& One, const String& Two)
{
char Concant [] = {};
int i = 0;
int i2 = 0;
while (i < One.length())
{
Concant[i] = One[i];
i++;
}
while (i2 < Two.length())
{
Concant[i] = Two[i2];
i++;
i2++;
}
return Concant;
}

bool operator==(const String& One, const String& Two)
{
bool Val = true;
for (int i = 0; i < One.length(); i++)
{
if (One[i] != Two[i])
{
Val = false;
}
}
return Val;
}

bool operator<(const String& One, const String& Two )
{
if (One.length() < Two.length())
{
return true;
}
else
{
return false;
}
}

ostream& operator<<( ostream& Stream, const String& One)
{
int i;
for (i = 0; i < One.length(); i++)
{
Stream << One[i];
}
return Stream;
}

istream& operator>>(istream& Stream, String& One)
{
char InputString [] = {};

Stream >> InputString;
int i;
for (i = 0; i < strlen(InputString); i++)
{
One[i] = InputString[i];
}
return Stream;
}

[helios]

You're defining the function wrong in the .cpp.
It's not
String::String& operator=( const String& Copy){
It's
String& String::operator=( const String& Copy){

The same goes for all the other functions. They're all missing the scope.