c++14 - C++: same code and compiler, but different output after each build -

greetings stackoverflow's community! need someone's help.
here code supposed print 2 integers, first , last indexes of shortest sentence's symbols in string given (str). can see, shortest sentence in string "hey!!!"; character 'h' has index 16 , last exclamation mark has index 21, correct output should be: 16 21.
i've compiled code using cppshell (cpp.sh) , here's deal: same code compiled same compiler gives different result @ each new attempt build it:

attempt #1: 16 21
attempt #2: 145921712 4196790
attempt #3: 16 21
attempt #4: 16 21
attempt #5: 1453219648 4196790
etc.

please explain me strange situation? i'm novice @ c++, therefore may not see obvious mistakes in code.

#include <iostream> #include <cstdlib> #include <clocale> #include <cstdio> #include <cstring>  using namespace std;  int main() {     setlocale(lc_ctype, "rus");      char str[] = "     what's up? hey!!!    it's practice... how you??    ";     char* ptr = str;     char* p = ptr;      int startsym, endsym;     int startsymmin = 0, endsymmin = 2000;       while(*ptr)     {         if (*ptr > 64 && *ptr < 91) // capitalized letters 'a'-'z'         {             startsym = strchr(ptr, *ptr)-p;              while(*ptr)             {                 if ((*ptr == '!' && *(ptr+1) != '!' && *(ptr+1) != '?')                     || (*ptr == '?' && *(ptr+1) != '!' && *(ptr+1) != '?')                     || (*ptr == '.' && *(ptr+1) != '.'))                 {                     endsym = strchr(ptr, *ptr)-p;                     break;                 }                 ptr++;             }         }          if (endsym - startsym < endsymmin - startsymmin) {             startsymmin = startsym;             endsymmin = endsym;         }          ptr++;     }      cout << startsymmin << " " << endsymmin << endl;      return 0; } 

look @ first iteration of loop. first if false, @ second if, use variables (startsym, endsym) not initialized.

initialize these variables well, , program work ok. sample string, @ least (i think need solve other edge cases make program work ok every strings).

tips:

• use debugger find out why program misbehaves (but, unfortunately, in particular case, debugger may not tell what's problem).
• if use msvc, can turn on run-time checks uninitialized variables (/rtcu)
• if use linux, can use valgrind catch error (and lot of other kind of errors)