Question

When I try to assign to individual characters in a string with s[i] = c I get a compiler error:

string s = "bcc";
s[0] = 'a'; // shows compile time error - indexer cannot be assigned - it's readonly

However this works:

s.ToCharArray()[0] = 'a';

and we can also completely assign the string to acc:

s = "acc"

Answer 1

This:

s="acc"

… is changing the value of the variable to refer to a different string. If this were allowed:

s[0] = 'a';

that wouldn’t be changing the value of the variable – it would have to change the contents of the string that s referred to. Strings are immutable in .NET, so that’s not allowed.

It’s important to differentiate between changing the value of a variable and changing the data within the object it refers to.

Changing the contents of s.ToCharArray() doesn’t do anything to either s or the string – it just mutates the newly-created array which is a copy of the data within the string.