Function not declared in scope

[Winsu]

I have made a class and I have an operator overloaded...I have a few members functions (they are members because they use the member data)....I have declared a function which doesn't use any member data and that function is used by the operator += which is overloaded in the class....what happens is when I compile the program the compiles says to me that that function was not declared in the scope...I could do that function a member, but I wouldn't like to do that..how could i do it?? here I post what matter of the program.....

To summarize...I would like to make visible that function without making a member of the class becasue in fact expand function( is the one) doesn't get any member data...

 class String{
private:
	static const int short_max = 15;
	int sz;
	char* ptr;
	union{
		int space;
		char ch[short_max +1];
	};
	void check(int n) const{
		if(n<0 or sz<=n){
			throw std::out_of_range("String::at()");
		}
	}
	
	void copy_from(const String& x);
	void move_from(String& x);

public:


	String():sz{0},ptr{ch}{
		ch[0] = 0;
	}
	
String(const char* p):sz{strlen(p)},ptr{(sz<=short_max)?ch : new char[sz +1]},space{0}{
	strcpy(ptr,p);
}

tring& operator+=(char c){
	if(sz==short_max){
		int n = sz+sz+2;
		ptr = expand(ptr,n);   //expand was not declared in this scope
		space = n-sz-2;
	}
	else if(short_max<sz){
		if(space==0){
			int n = sz + sz + 2;
			char* p = expand(ptr,n);  //expand was not declared in 
			delete[] ptr,             //in this scope
			space = n-sz-2;
		}
	else
		--space;
	}
ptr[sz] = c;
ptr[++sz] = 0;

return *this;
}
	
};

	char* expand(const char* ptr,int n){ 		//allocate memory for a string bigger than short_max
	char* p = new char[n];
	strcpy(p,ptr);
	return p;
}

[AbstractionAnon]

Line 13: #include <stdexcept> missing

Line 30: You're missing the S in String.

Line 54: You either need to declare expand as a member of String, or provide a forward declaration for it. At the point the compiuler processes line 39, it does not know what expand looks like.

[Winsu]

but that forward declaration wouldn't have to be in the class scope, would it?

[Winsu]

yes, It doesn't thanks