What Does printf & scanf return?

printf returns the number of characters it prints. 

Examples:

If you write an expression like:

x = printf("%s", "Muttley is awesome!"); or

y = printf("%d", 1111);

then, what does printf return to x and y?

x = 19 and y = 4.

scanf returns the number of items it scans. However it stops scanning as soon as you give wrong input.

Examples:

p = scanf("%d%d%d", &y, &z, &w);

r = scanf("%d%d", &y, &z);

If all inputs are correct in the expression for p then, 

p = 3. Similarly, r = 2.

Lets say you give wrong third input(may be you enter a character instead of int) in the expression for p, immediately scanf stops and returns the value 2 to p. If the first input is wrong then scanf will return 0 to p.

So we can say that scanf returns the number of items scanned before the first wrong input entered. 

(Reminds me of geometric distribution)