macOS how to capitalize character at specified index in string?

[i.yalovecky]

subj, thanks.

 

[b0redom]

erm, in what language?

 

[gnasher729]

subj, thanks.

Please tell us what it is that you actually try to achieve. The question that you are asking suggests that you are on a very, very wrong path to doing whatever you want to do.

 

[kainjow]

See:

NSMutableString
replaceCharactersInRange:withString:
uppercaseString