
The most common prompt type is a number. Numbers can be either integers or reals. Valid numbers are, for example, 16, 2.4, .9E5, and +1E5. Integers can also be specified in binary, octal, and hexadecimal form. The decimal integer 31 can be entered as 31, #b11111, #o37, or #x1f. In Scheme, integers are a subset of reals, so you do not need a decimal point to indicate that a number is real; 2 is just as much a real as 2.0. If you enter a real at an integer prompt, any fractional part will simply be truncated; 1.9 will become 1.