string - Why does the output of this C++ program produce a giant mess in cmd? -

i have since figured out how make program correct, wondering why incorrect program question follows produces whole bunch of characters , different machine information, , if such error damage machine:

exercise 3.10: write program reads string of characters including punctuation , writes read punctuation removed.

#include <iostream> #include <string> using std::string; using std::cin; using std::cout; using std::endl;   int main() {     string s("some! string!s.");       (decltype(s.size()) index = 0;         index != s.size(); ++index){             if (!ispunct(s[index])){                 cout << s[index];                 ++index;             }             else {                 ++index;             }         }      return 0; } 

now, know incorrect, , have since made version correctly output needed:

#include <iostream> #include <string> using std::string; using std::cin; using std::cout; using std::endl;   int main() {     string s("some! string!s.");       (decltype(s.size()) index = 0;         index != s.size(); ++index){             if (!ispunct(s[index])){                 cout << s[index];             }         }      return 0; } 

why did first 1 produce mess of code? also, when there if , no else, thought when reaches "empty" or non-existing else stops; why, in second program, move on next character , restarts loop after hitting empty else?

• your string 15 characters long.
• the incorrect code increments character index 2 on each iteration rather 1.
• you're terminating loop when index exactly equal length of string (15) rather testing out-of-bounds condition.
• when character index 14 (corresponding '.' character) index increment 16, length of string 15, 16 != 15 loop continues , undefined memory past end of string read , written output stream.