A macro isn't a function, it's inline assembly. You put this into the compuler...
Code:
strcpy(s, "rstu");
i=0;
putchar(TOUPPER (s[++i]); /* call of macro */
And your compiler has to read the code twice. First, it goes through and takes care of all the macros and definitions, changing the former code into this...
Code:
strcpy(s, "rstu");
i=0;
putchar(
('a' <= (s[++i]) && (s[++i]) <= 'z' ?
(s[++i]) - 'a' + 'A' : (s[++i]))
); /* call of macro */
Broke the macro onto several lines for viewability. Hope that doesn't confuse...
Now, that beast of a line that the preprocessor threw into our putchar is what actually gets compiled, so let's just go through it....
1. 'a' <= (s[++i]) // ++i, then 'a' <= s[1] TRUE
2. (s[++i]) <= 'z' // ++ i, then s[2] <= 'z' TRUE
3. s[++i] - 'a' + 'A' // ++i, then return s[3] - 'a' + 'A', which is U
I get it !!
