Data Types Examples in CS Thinking
Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Data Types.
This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in CS Thinking.
Concept Recap
Categories that classify data values and determine which operations can validly be performed on them. Common data types include integers, floating-point numbers, strings, booleans, and arrays, each with its own set of permitted operations.
Different kinds of data (numbers, text, true/false) work differently.
Read the full concept explanation →How to Use These Examples
- Read the first worked example with the solution open so the structure is clear.
- Try the practice problems before revealing each solution.
- Use the related concepts and background knowledge badges if you feel stuck.
What to Focus On
Core idea: Operations depend on type: you can add numbers, concatenate strings.
Common stuck point: '5' (text) and 5 (number) are different—some languages convert automatically, some don't.
Sense of Study hint: When working with data types, always check what type a value is before performing operations on it. If you need to combine different types (e.g., a number and a string), explicitly convert one to match the other. Use your language's type-checking tools to catch mismatches early.
Worked Examples
Example 1
easyClassify each value into its data type: (a) 42, (b) 'Hello', (c) 3.14, (d) TRUE.
Answer
(a) Integer, (b) String, (c) Float/Real, (d) Boolean.
First step
1
Step 1: 42 is a whole number with no decimal point — this is an integer.
Full solution
- 2 Step 2: 'Hello' is text enclosed in quotes — this is a string.
- 3 Step 3: 3.14 has a decimal part — this is a float (real number). TRUE is a logical value — this is a boolean.
Data types define what kind of value a variable holds and what operations can be performed on it. The four fundamental types are integer, float, string, and boolean.
Example 2
mediumA program reads user input as a string '25'. What happens if you try to calculate '25' + 10 without type conversion? What should you do instead?
Example 3
easyClassify each: (a) 100, (b) 'OK', (c) 2.5, (d) true, (e) [1,2].
Example 4
mediumFor each scenario, choose the most appropriate data type: (a) phone number, (b) age in years, (c) account balance in dollars, (d) is_member?
Example 5
hardWhy might equal in floating point, and what is one common workaround?
Example 6
hardA shop tracks prices as integer cents to avoid floating-point error. A bag of apples costs . Store it as what integer, and what is the total cents for bags?
Example 7
challengeSorting strings ['9','10','100','2'] lexicographically vs numerically gives different orders. Show both sorted lists.
Practice Problems
Try these problems on your own first, then open the solution to compare your method.
Example 1
mediumFor each scenario, choose the most appropriate data type: (a) a student's name, (b) number of students in a class, (c) whether a student passed, (d) a student's average grade (e.g., 87.5).
Example 2
hardA program stores prices as integers in pence (e.g., 499 for £4.99) rather than as floats. Explain two advantages of this approach.
Example 3
easyWhat data type is the value true?
Example 4
easyWhat data type is the value 'hello'?
Example 5
easyWhat data type is the value 42?
Example 6
easyWhat data type is the value 3.14?
Example 7
easyWhich operation joins two strings: addition (concatenation) or subtraction?
Example 8
easyAre '5' (a string) and 5 (an integer) the same data type? Yes or no.
Example 9
easyWhat type results from comparing 3 < 5?
Example 10
easyWhat data type is a collection like [1, 2, 3]?
Example 11
mediumIn a language with integer division, what is as integer division?
Example 12
mediumWhat is the result of '3' + '4' when both are strings?
Example 13
mediumUser input arrives as the string '10'. To add 5 numerically, what must you do first, and what is the result?
Example 14
mediumWhat is (the modulo/remainder operation)?
Example 15
mediumAdding an integer 5 and a float 2.5 gives what type and value?
Example 16
mediumA list stores [1, 'two', 3.0]. What are the types of its three elements in order?
Example 17
mediumWhy does comparing 0.1 + 0.2 == 0.3 sometimes return false in floating-point?
Example 18
mediumWhat is the length (number of characters) of the string 'hello'?
Example 19
mediumIndex into the string 'CODE' at position 0 (zero-based). What character is returned?
Example 20
challengeA program reads ['3','1','2'] (strings) and sorts them; then reads [3,1,2] (ints) and sorts. Both sort fine here, but when would string vs int sorting differ? Give the order for ['10','9','2'].
Example 21
challengeA function expects an integer count but receives the float 4.0. It uses count as a list size. Why might this error, and what is the safe fix?
Example 22
challengeBooleans are often treated as numbers: true=1, false=0. What does true + true + false evaluate to under this rule?
Example 23
easyWhat data type is the value ?
Example 24
easyWhat data type is the value ?
Example 25
easyWhich operation joins 'cat' + 'fish' into 'catfish'?
Example 26
easyWhat type results from the comparison ?
Example 27
mediumIn a language with integer division, what is ?
Example 28
mediumWhat is the result of '7' + '8' when both are strings?
Example 29
mediumUser input '99' arrives as a string. To compare it numerically against , what conversion is needed, and is the converted value less than ?
Example 30
mediumAdding integer and float gives what type and value?
Example 31
mediumWhat is the length of the string 'computer'?
Example 32
mediumZero-based index 2 of 'PYTHON' returns which character?
Example 33
mediumWhat is the result of '5' * 3 in a language where string * int repeats the string?
Example 34
mediumList the types of the elements of [42, 'cat', 3.0, false] in order.
Example 35
hardIn integer division, what is if the language rounds toward negative infinity?
Example 36
hardA program reads ['100','20','3'] as strings and sorts them lexicographically. Give the sorted order.
Example 37
hardA function expects an integer index but receives the float . It uses the index for list[i]. Why is this often an error, and what is the safe fix?
Example 38
hardBooleans true=1, false=0. Evaluate true + false + true + true.
Example 39
challengeA function signature is f(name: string, age: int) -> bool. It is called as f('Sam', '14'). What is the type-error and what conversion would fix it?
Background Knowledge
These ideas may be useful before you work through the harder examples.
variable