C/C++ :: Replacing Character In String With Another Character

So I'm trying to create a function that replaces any instance of a character in a string with another. So first I tried the replace() string member function:

In my implementation file

void NewString::ReplaceChar(const char& target,const char& entry)
{
this->replace(this->begin(),this->end(), target, entry);
};

Main program

#include "NewString.h"
using namespace ...;
int main()

[Code].....

Instead of replacing the the l's with y's it outputted a long string of y's. Also, NewString is derived from the string class (it's for the assignment). the header and whole implementation file, already tested.

I've also tried, instead, to use a for loop in ReplaceChar() but I need to overload the == operator and I don't know how I should exactly:

bool NewString::operator ==(const char& target)const {
if(*this == target)
return true;

[Code]....

I want the == operator to test if the value in the char array is equal to target but I'm not sure how to pass in the position. I'm guessing the this pointer in ReplaceChar() is not the same as the one dereferenced in ==() because target is never replaced by entry in the string.