Log Message Timestamp

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

// Write your function here
void logMessage(string msg=nullptr,bool flag=false)
{
   if(flag){cout << "[123456] "<<msg;}
   else{cout << msg;}
}

int main() {
    int mode;
    string msg;
    cin >> mode >> msg;

    if (mode == 0) {
        logMessage(msg);            // use default argument
    } else {
        logMessage(msg, true);      // enable timestamp
    }

    return 0;
}

Solving Approach