Basic data types: values and permitted operations

A data type describes two things: which values can be stored and which operations are permitted. A number-shaped label, a mark and a name have different meanings even when a computer can store all their characters.

Boolean: True or False #

A Boolean has exactly two values: True and False. Conditions produce Booleans. For example, 68 > 50 is True; city = Chennai is True or False for a particular record. AND, OR and NOT combine or reverse these values.

Integer: whole numbers including negatives #

Integers are …,−3,−2,−1,0,1,2,3,… . Adding, subtracting and multiplying integers gives an integer. Comparisons such as <, > and = give a Boolean, not another mark or count.

Division needs a stated rule #

21 divided by 7 gives integer 3 exactly. For 22 divided by 7, you may either allow a fractional result or explicitly choose the integer quotient 3 and remainder 1. The lecture discusses requiring exact divisibility or keeping the quotient. Do not silently use a quotient when an average needs its fractional part. Division by zero is never allowed here; rules for negative quotients also need specification in a concrete language.

Character and string #

A character is one symbol, such as A, z, 7, a comma or a full stop. A string is a sequence of characters, such as Chennai. The character “7”, the string “72” and the integer 72 are different kinds of values. Comparing two characters or strings for equality gives a Boolean.

The lecture uses a check on the last character of a word to detect a full stop. That is a rule for this dataset’s sentence endings; abbreviations, question marks and other punctuation would require a richer rule in general text.

Input type and result type can differ #

Source: Lecture 1.7 — Introduction to datatypes. Small teaching datasets and diagrams are prepared for these notes; lecture and tutorial totals are identified explicitly.