d is for dinteger, obviously. Edit: Actually, I finally remembered why I always use %d, and why I find seeing %i odd. While %d and %i may be the same for outpu

d is for dinteger, obviously. Edit: Actually, I finally remembered why I always use %d, and why I find seeing %i odd. While %d and %i may be the same for output with printf, they are different for input with scanf. (Also I'm not sure that %i was part of the C89/90 standard for printf, it may have been a compiler specific thing (another reason to avoid); it's defined in C99 but I don't have a copy of the 89/90 pdf.)