Working with Text

This surprises a lot of beginners coming from other languages: C has no built-in string type. Instead, text is represented as an array of char values, with a special hidden character '\0' (the "null terminator") marking where the text ends. Every C string-handling function relies on that terminator to know when to stop reading.

A string literal like "Hello" is stored read-only by the compiler. You can look at it and copy from it, but you can't modify its characters directly. To build or change text at runtime, you declare a char array (a buffer) with enough room, and copy or append into that buffer instead.

Include <string.h> to get functions like strlen() (length) and strcat() (concatenate/append). strcat(greeting, name) appends name's characters onto the end of greeting, right up to (and replacing) greeting's terminator, which only works safely if greeting's buffer was declared with enough spare room to fit the result, as it is here with char greeting[20].