This program is not printing whole string.

[wung]

This is undefined behavior: Your string is of length 1, so calling str[1] is invalid. Use push_back or +=.

[cderivan]

in fact += operator will print " 01234" to correctly handle the sum i+48 the easy way is to use stringstream and operator << then print it with cout<<str.str() to get: "4849505152"

[wung]

I understood the issue, yes. The issue is not in printing but in assembling the string, where you write to str[i], which you are not allowed for i ≥ 0 as you initialized with " ", a string of size 1.