c++ - Simple program with std::string is not working -

i learning std::string , want :

1. input string
2. every second letter make uppercase

3. output new string

   #include "stdafx.h"  #include <iostream> #include <string> using namespace std; int main() {     string mystr;     getline(cin,mystr);     if (mystr.begin() != mystr.end())     {         (auto = mystr.begin(); != mystr.end() ; += 2)             *it = toupper(*it);      }     cout << mystr;     system("pause");     return 0; } 

   but after input getting error here:

it += 2 leads out of bounds, if loop ending condition it != mystr.end(). dereferencing

*it = toupper(*it);  

is undefined behavior.

it += 2 never give exact iterator value of mystr.end() have loops termination condition.

---

as comment:

so how can fix ?

just keep simple , understandable, e.g. using like

for (size_t = 0; < mystr.length() ; ++i) {     if(i % 2) { // every second letter ...         mystr[i] = toupper(mystr[i]);      } }