C++, best way to change a string at a particular index

Assigning a character to an std::string at an index will produce the correct result, for example:

#include <iostream>
int main() {
    std::string s = "abc";
    s[1] = 'a';
    std::cout << s;
}

For those of you below doubting my IDE/library setup, see jdoodle demo: http://jdoodle.com/ia/ljR, and screenshot: https://imgur.com/f21rA5R

Which prints aac. The drawback is you risk accidentally writing to un-assigned memory if string s is blankstring or you write too far. C++ will gladly write off the end of the string, and that causes undefined behavior.

A safer way to do this would be to use string::replace: http://cplusplus.com/reference/string/string/replace

For example

#include <iostream> 
int main() { 
    std::string s = "What kind of king do you think you'll be?"; 
    std::string s2 = "A good king?"; 
    //       pos len str_repl 
    s.replace(40, 1, s2); 
    std::cout << s;   
    //prints: What kind of king do you think you'll beA good king?
}

The replace function takes the string s, and at position 40, replaced one character, a questionmark, with the string s2. If the string is blank or you assign something out of bounds, then there's no undefined behavior.

Yes the code you have written is valid. You can also try:

string num;
cin>>num;
num.at(1)='a';
cout<<num;

**Input**:asdf
**Output**:aadf

the std::replace can also be used to replace the charecter. Here is the reference link http://www.cplusplus.com/reference/string/string/replace/

Hope this helps.

Yes. The website you link has a page about it. You can also use at function, which performs bounds checking.

http://www.cplusplus.com/reference/string/string/operator%5B%5D/