c++ - Adding null character after string computation -

i trying print string "ans" directly using

cout << ans; 

instead of going through loop on each character of string. here complete code have written (string ans , s have same size).

ps: program takes string , print corresponding number associated character of mobile keypad.(like b c give 2, d e f give 3)

(so string abcdef print 222333 why string ans , s have same size)

ps: have written in comments problem is.

#include<iostream> char has[]={'2','2','2','3','3','3','4','4','4','5','5','5','6','6','6','7','7','7','7','8','8','8','9','9','9','9'}; using namespace std; int main()  {     //code          int t;          cin>>t;           while(t)          {             string s,ans;             int i;             cin>>s;             for(i=0;i<s.length();i++)             {                 ans[i]=has[s[i]-'a'];             }             ans[i]='\0';             cout<<ans;  // **does not printing string "ans" why?****              for(i=0;i<s.length();i++)              cout<<ans[i];  // **printing string "ans" using loop**              cout<<endl;             //**some other methods found in forum commented them**             //string str(ans);             //cout<<str.c_str();                t--;          }     return 0; } 

a std::string initialized empty string. accessing ans via operator[], not add characters string. accessing non-existing indices way undefined behaviour, unfortunately didn't cause crash hint error.

possible solutions: initialize string needed length if want keep on using operator[] or use std::stringstream form needed string.

btw: std::string doesn't need terminating nul-character.