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1. Keep your includes ordered. Thus, you won't lose track of them, even if there are more of them.

   Common order is (all sections sorted alphabetically, separating empty line optional):

   1. precompiled header if applicable, for technical reasons
   2. the corresponding header, to ensure it is self-contained
   3. standard headers
   4. other library headers, though may be merged with previous section
   5. Own headers

4. Don't name arguments you won't use. Thus, you avoid confusing future readers (like yourself) nor cause spurious warnings.
   In the case of main(), you might just leave the arguments out completely.

5. Don't muzzle the compiler just because it has the audacity to warn you. Figure out what you did wrong instead, and fix that. Yes, sometimes you have to override it, but you have to be judicious and careful there, using the least dangerous tool to get the job done.
   In the specific case, instead of casting away const, fix the pointer type. const_cast would have been less dangerous than an unrestricted C-style cast, if it had been appropriate.

6. Embrace auto. Almost Always Auto is a good idea to avoid mismatches and unintended conversions, especially if the exact type doesn't matter to you.

7. Only use std::endl when you need to flush the stream. Actually, belay that, be explicit and use std::flush.
   Also, when the program ends the standard streams are flushed.
   See "What is the C++ iostream endl fiasco? ".

8. return 0; is implicit for main().

1. Keep your includes ordered. Thus, you won't lose track of them, even if there are more of them.

   Common modern order goes from local to universal, to ensure headers are self-contained. Exceptions are fixed or at least annotated. All groups are sorted and separated by an empty line for emphasis:

   1. precompiled header if applicable, for obvious technical reasons
   2. the corresponding header, to ensure it is self-contained
   3. own headers
   4. external libraries headers
   5. system headers
   6. standard headers

   Any of the last three might be amalgamated.

4. Don't name arguments you won't use. Thus, you avoid confusing future readers (like yourself) nor cause spurious warnings.
   In the case of main(), you might just leave the arguments out completely.

5. Eliminate dead code and dead variables. They will just confuse, and if you want to restore them, there is source control. Let the compiler warn you about them as it can.

6. Don't muzzle the compiler just because it has the audacity to warn you. Figure out what you did wrong instead, and fix that. Yes, sometimes you have to override it, but you have to be judicious and careful there, using the least dangerous tool to get the job done.
   In the specific case, instead of casting away const, fix the pointer type. const_cast would have been less dangerous than an unrestricted C-style cast, if it had been appropriate.

7. Embrace auto. Almost Always Auto is a good idea to avoid mismatches and unintended conversions, especially if the exact type doesn't matter to you.

8. Only use std::endl when you need to flush the stream. Actually, belay that, be explicit and use std::flush.
   Also, when the program ends the standard streams are flushed.
   See "What is the C++ iostream endl fiasco? ".

9. return 0; is implicit for main().

4. Don't name arguments you won't use. Thus, you avoid confusing future readers (like yourself) nor cause spurious warnings.
   In the case of main(), you might just leave the arguments out completely.

5. Don't muzzle the compiler just because it has the audacity to warn you. Figure out what you did wrong instead, and fix that. Yes, sometimes you have to override it, but you have to be judicious and careful there, using the least dangerous tool to get the job done.
   In the specific case, instead of casting away const, fix the pointer type. const_cast would have been less dangerous than an unrestricted C-style cast, if it had been appropriate.

6. Embrace auto. Almost Always Auto is a good idea to avoid mismatches and unintended conversions, especially if the exact type doesn't matter to you.

7. Only use std::endl when you need to flush the stream. Actually, belay that, be explicit and use std::flush.
   Hint: std::cin and std::cout are tied, which you already take advantage of with your prompt. Also, when the program ends the standard streams are flushed.
   See "What is the C++ iostream endl fiasco? ".

8. return 0; is implicit for main().

4. Don't name arguments you won't use. Thus, you avoid confusing future readers (like yourself) nor cause spurious warnings.
   In the case of main(), you might just leave the arguments out completely.

5. Don't muzzle the compiler just because it has the audacity to warn you. Figure out what you did wrong instead, and fix that. Yes, sometimes you have to override it, but you have to be judicious and careful there, using the least dangerous tool to get the job done.
   In the specific case, instead of casting away const, fix the pointer type. const_cast would have been less dangerous than an unrestricted C-style cast, if it had been appropriate.

6. Embrace auto. Almost Always Auto is a good idea to avoid mismatches and unintended conversions, especially if the exact type doesn't matter to you.

7. Only use std::endl when you need to flush the stream. Actually, belay that, be explicit and use std::flush.
   Also, when the program ends the standard streams are flushed.
   See "What is the C++ iostream endl fiasco? ".

8. return 0; is implicit for main().

1. Keep your includes ordered. Thus, you won't lose track of them, even if there are more of them.

   Common order is (all sections sorted alphabetically, separating empty line optional):

   1. precompiled header if applicable, for technical reasons
   2. the corresponding header, to ensure it is self-contained
   3. standard headers
   4. other library headers, though may be merged with previous section
   5. Own headers

2. Don't bolt your own operators on someone else's type. It just invites confusion. Use a properly named free function instead.

3. Using C++17 std::string_view leads to a more efficient and convenient interface, and simplifies your implementation.

4. Avoid special cases. They mean more code (which can be wrong), and slow down the common case.

   #include <iostream>
   #include <string>
   #include <string_view>
   std::string replace_placeholder(std::string_view format, std::string_view a) {
    auto pos = format.find('$');
    auto rest = pos + 1;
    std::string r;
    r.reserve(format.size() + a.size() - (pos != std::string_view::npos));
    if (pos == std::string_view::npos)
    rest = pos = format.size();
    r.append(format.begin(), format.begin() + pos);
    r += a;
    r.append(format.begin() + rest, format.end());
    return r;
   }
   

5. Don't name arguments you won't use. Thus, you avoid confusing future readers (like yourself) nor cause spurious warnings.
   In the case of main(), you might just leave the arguments out completely.

6. Don't muzzle the compiler just because it has the audacity to warn you. Figure out what you did wrong instead, and fix that. Yes, sometimes you have to override it, but you have to be judicious and careful there, using the least dangerous tool to get the job done.
   In the specific case, instead of casting away const, fix the pointer type. const_cast would have been less dangerous than an unrestricted C-style cast, if it had been appropriate.

7. Embrace auto. Almost Always Auto is a good idea to avoid mismatches and unintended conversions, especially if the exact type doesn't matter to you.

8. Only use std::endl when you need to flush the stream. Actually, belay that, be explicit and use std::flush.
   Hint: std::cin and std::cout are tied, which you already take advantage of with your prompt. Also, when the program ends the standard streams are flushed.
   See "What is the C++ iostream endl fiasco? ".

9. return 0; is implicit for main().

   int main() {
    std::string string = "Hello ,ドル My name is Ben!";
    auto cstr = "World";
    auto result = replace_placeholder(string, cstr);
    std::cout << result << "\n";
   }
   

1. Keep your includes ordered. Thus, you won't lose track of them, even if there are more of them.

   Common order is (all sections sorted alphabetically, separating empty line optional):

   1. precompiled header if applicable, for technical reasons
   2. the corresponding header, to ensure it is self-contained
   3. standard headers
   4. other library headers, though may be merged with previous section
   5. Own headers

#include <iostream>
#include <string>
#include <string_view>

2. Don't bolt your own operators on someone else's type. It just invites confusion. Use a properly named free function instead.

3. Using C++17 std::string_view leads to a more efficient and convenient interface, and simplifies your implementation.

4. Avoid special cases. They mean more code (which can be wrong), and slow down the common case.

std::string replace_placeholder(std::string_view format, std::string_view a) {
 auto pos = format.find('$');
 auto rest = pos + 1;
 std::string r;
 r.reserve(format.size() + a.size() - (pos != std::string_view::npos));
 if (pos == std::string_view::npos)
 rest = pos = format.size();
 r.append(format.begin(), format.begin() + pos);
 r += a;
 r.append(format.begin() + rest, format.end());
 return r;
}

4. Don't name arguments you won't use. Thus, you avoid confusing future readers (like yourself) nor cause spurious warnings.
   In the case of main(), you might just leave the arguments out completely.

5. Don't muzzle the compiler just because it has the audacity to warn you. Figure out what you did wrong instead, and fix that. Yes, sometimes you have to override it, but you have to be judicious and careful there, using the least dangerous tool to get the job done.
   In the specific case, instead of casting away const, fix the pointer type. const_cast would have been less dangerous than an unrestricted C-style cast, if it had been appropriate.

6. Embrace auto. Almost Always Auto is a good idea to avoid mismatches and unintended conversions, especially if the exact type doesn't matter to you.

7. Only use std::endl when you need to flush the stream. Actually, belay that, be explicit and use std::flush.
   Hint: std::cin and std::cout are tied, which you already take advantage of with your prompt. Also, when the program ends the standard streams are flushed.
   See "What is the C++ iostream endl fiasco? ".

8. return 0; is implicit for main().

int main() {
 std::string string = "Hello ,ドル My name is Ben!";
 auto cstr = "World";
 auto result = replace_placeholder(string, cstr);
 std::cout << result << "\n";
}