Step by Step solution about How to resolve the algorithm Selectively replace multiple instances of a character within a string step by step in the C++ programming language

The provided code is a C++ program that performs a substitution cipher on a string called magic using a provided map. Here's a detailed explanation of the code:

• Map Initialization: The program starts by initializing a map named rep of character keys and string values. This map represents the substitution rules for the cipher. For instance:

  • The key 'a' maps to the string "DCaBA". This means that every 'a' in the input string will be replaced by "DCaBA" in the output string.
  • The key 'b' maps to the string "E". This means every 'b' in the input string will be replaced by "E" in the output string.
  • The key 'r' maps to the string "Fr". This means every 'r' in the input string will be replaced by "Fr" in the output string.

• Input String: The program defines a string variable magic with the value "abracadabra". This is the input string on which the substitution cipher will be applied.

• Iterating Over the Input String: The program enters a loop that iterates through each character of the input string magic.

• Checking for Substitution: For each character *it in the input string, the program checks if there's an entry for that character in the rep map. It does this using the find(*it) method. If a matching entry is found and the corresponding replacement string is not empty, the following steps are taken:

  • The character *it in the input string is replaced with the last character of the replacement string.
  • The last character is removed from the replacement string to prepare for the next substitution of the same character.

• Output: After processing all characters in the input string, the program prints the modified magic string, which represents the ciphered text.

In this specific example, the program will perform the following substitutions:

• 'a' in "abracadabra" is replaced by "DCaBA" (reversed) -> "abDCaBAracadabra"
• 'b' in "abDCaBAracadabra" is replaced by "E" -> "aEDCaBAracadabra"
• 'r' in "aEDCaBAracadabra" is replaced by "Fr" -> "aEFrDCaBAracadabra"

The final output will be "aEFrDCaBAracadabra".

#include <map>
#include <iostream>
#include <string>

int main()
{
  std::map<char, std::string> rep = 
    {{'a', "DCaBA"}, // replacement string is reversed
     {'b', "E"},
     {'r', "Fr"}};

  std::string magic = "abracadabra";

  for(auto it = magic.begin(); it != magic.end(); ++it)
  {
    if(auto f = rep.find(*it); f != rep.end() && !f->second.empty())
    {
      *it = f->second.back();
      f->second.pop_back();
    }
  }

  std::cout << magic << "\n";
}