scanf_whitespace.md

Handling Whitespace in scanf

When the user presses space or enter in the console, this puts ' ' and '\n' whitespace characters into stdio respectively. When reading an int* with %d or float* with %f, scanf skips any leading whitespace. However, %c for char* extracts whitespace characters.

Example Problem

Say the user enters " 70 f", and we want to read 70 and f into int and char respectively:

int x; char c;
scanf("%d", &x); // OK,  x = 70
scanf("%c", &c); // BAD, c = ' '

Instead of reading f, we read a space, because %c does not skip leading whitespace. Solution:

scanf(" %c", &c);

The leading space before %c matches any whitespace of any length.