Replacing letters in a string by other ones

[yup2]

Im having trouble replacing letters of the alphabet with one and other,
for instance: A->E
B->R and so on..
I've been using the following code:

   std::replace( s.begin(), s.end(), 'a', 'e');
  std::replace( s.begin(), s.end(), 'b', 'r');
  std::replace( s.begin(), s.end(), 'm', 'a');

However from my understanding it seems like what ever is replaced will once again get replaced as I keep calling replace. My question is how could I do this to replace the characters in std::string all at once? I've tried making the string a constant but other than that I am stuck.

Thank you in advanced for your help!

[lastchance]

#include <iostream>
#include <string>
using namespace std;

void encode( char &c )
{
   switch( c )
   {
      case 'a':   c = 'e';   return;
      case 'b':   c = 'r';   return;
      case 'm':   c = 'a';   return;
   }
}

int main()
{
   string test = "abnormal behaviour";
   cout << test << '\n';
   for ( char &c : test ) encode( c );
   cout << test << '\n';
}

A little bit more flexible:

#include <iostream>
#include <string>
using namespace std;

void encode( char &c )
{
   string input  = "abm";
   string output = "era";
   size_t p = input.find( c );
   if ( p != string::npos ) c = output[p];
}

int main()
{
   string test = "abnormal behaviour";
   cout << test << '\n';
   for ( char &c : test ) encode( c );
   cout << test << '\n';
}

[yup2]

Thank you so much!

[seeplus]

Also:

#include <iostream>
#include <string>
#include <algorithm>

using name space std;

int main()
{
	string test = "abnormal behaviour";
	cout << test << '\n';

	std::transform(test.begin(), test.end(), test.begin(), [inp = "abm"s, out = "era"s, p = 0u](char ch) mutable {
		return (p = inp.find(ch)) != string::npos ? out[p] : ch; });

	cout << test << '\n';
}

giving as output:

abnormal behaviour
ernorael reheviour