The reason is readability, not disk space or typing speed. When your screen resolution is 24 lines of 80 characters (a common screen resolution back when C beca

The reason is readability, not disk space or typing speed. When your screen resolution is 24 lines of 80 characters (a common screen resolution back when C became popular), having longer variable names means statements often have to be split over several lines, and less code fits on the screen at the same time. Even today, having shorter lines makes it easier to see several versions of the code side-by-side (for instance, when doing a merge, it's not unusual to see three versions of the code at the same time).