Number type behavior in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of arithmetic with mixed number types

What is the output of this TypeScript code snippet?

Typescript

const a: number = 5;
const b: number = 2.5;
const c = a + b;
console.log(c);

A 7

B 7.5

C TypeError

D NaN

💡 Hint

Remember that TypeScript's number type includes both integers and decimals.

In TypeScript, the number type covers all numeric values including decimals. Adding 5 and 2.5 results in 7.5.

❓ Predict Output

intermediate

Result of dividing by zero

What will this TypeScript code output?

Typescript

const x = 10 / 0;
console.log(x);

A Infinity

B NaN

C 0

D Throws an error

💡 Hint

Think about how JavaScript and TypeScript handle division by zero.

Dividing a positive number by zero in TypeScript results in Infinity, not an error.

❓ Predict Output

advanced

Output of bitwise operation on numbers

What is the output of this code?

Typescript

const a = 5; // binary 0101
const b = 3; // binary 0011
const c = a & b;
console.log(c);

A 8

B 7

C 1

D TypeError

💡 Hint

Bitwise AND compares each bit of the numbers.

5 in binary is 0101, 3 is 0011. Bitwise AND is 0001 which is 1 in decimal.

❓ Predict Output

advanced

Behavior of Number.MAX_SAFE_INTEGER + 1

What is the output of this TypeScript code?

Typescript

console.log(Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2);

A undefined

B false

C Throws an error

D true

💡 Hint

Consider the precision limits of JavaScript numbers.

Numbers beyond MAX_SAFE_INTEGER lose precision, so adding 1 or 2 results in the same value.

❓ Predict Output

expert

Output of floating point addition precision

What is the output of this code snippet?

Typescript

const a = 0.1 + 0.2;
console.log(a === 0.3);

A false

B true

C TypeError

D NaN

💡 Hint

Think about how floating point numbers are stored in computers.

Due to floating point precision errors, 0.1 + 0.2 is not exactly 0.3, so the comparison is false.

Practice

1.

In TypeScript, which of the following is true about the number type?

easy

A. It represents both whole numbers and decimals using the same type.

B. It only represents whole numbers (integers).

C. It only represents decimal numbers (floats).

D. You must declare separate types for integers and decimals.

Solution

1. Step 1: Understand TypeScript number type

   TypeScript uses a single number type for all numeric values, whether whole or decimal.

2. Step 2: Compare options with this fact

   Only "It represents both whole numbers and decimals using the same type." correctly states that both whole and decimal numbers share the same number type.

3. Final Answer:

   It represents both whole numbers and decimals using the same type. -> Option A

4. Quick Check:

   TypeScript number = whole + decimal [OK]

Hint: Remember: one number type covers all numeric values [OK]

Common Mistakes:

• Thinking integers and decimals have separate types
• Assuming number type is only for floats
• Believing you must declare int or float explicitly

2.

Which of the following is the correct way to declare a variable x as a number with value 42 in TypeScript?

?

easy

A. let x: number = "42";

B. let x = "42";

C. let x: number = 42;

D. let x: string = 42;

Solution

1. Step 1: Check variable declaration syntax

   In TypeScript, to declare a number variable, use let x: number = value;.

2. Step 2: Validate each option

   let x: number = 42; correctly declares x as a number with value 42. Other options use wrong types or values, such as assigning a string to a number type, which is invalid.

3. Final Answer:

   let x: number = 42; -> Option C

4. Quick Check:

   Correct number declaration = let x: number = 42; [OK]

Hint: Use let x: number = value; for numbers [OK]

Common Mistakes:

• Assigning string values to number variables
• Missing the type annotation when needed
• Using quotes around numeric values

3.

What is the output of the following TypeScript code?

const a: number = 5;
const b: number = 2.5;
const c = a + b;
console.log(c);

medium

A. 7

B. Error

C. 52.5

D. 7.5

Solution

1. Step 1: Add the two numbers

   Variable a is 5 (integer), b is 2.5 (decimal). Adding gives 5 + 2.5 = 7.5.

2. Step 2: Check console output

   The console.log(c) prints the sum, which is 7.5.

3. Final Answer:

   7.5 -> Option D

4. Quick Check:

   5 + 2.5 = 7.5 [OK]

Hint: Add numbers normally; decimals stay decimals [OK]

Common Mistakes:

• Treating numbers as strings and concatenating
• Rounding automatically to integers
• Expecting a syntax or runtime error

4.

Identify the error in this TypeScript code snippet:

let num: number = 10;
num = "20";
console.log(num);

medium

A. Assigning a string to a variable declared as number causes a type error.

B. The variable num should be declared with const instead of let.

C. The console.log statement is missing parentheses.

D. There is no error; the code runs fine.

Solution

1. Step 1: Check variable type and assignment

   num is declared as number, but assigned a string "20" later, which is invalid in TypeScript.

2. Step 2: Identify the error type

   This causes a type error because TypeScript enforces type safety.

3. Final Answer:

   Assigning a string to a variable declared as number causes a type error. -> Option A

4. Quick Check:

   Type mismatch error = assigning string to number [OK]

Hint: Match variable type and assigned value exactly [OK]

Common Mistakes:

• Ignoring type mismatch errors
• Thinking TypeScript allows implicit type changes
• Confusing let and const as error causes

5.

Consider the following TypeScript code:

const values = [1, 2.5, 3, 4.75];
const integersOnly = values.filter(v => Number.isInteger(v));
console.log(integersOnly);

What will be the output?

hard

A. [1, 2.5, 3, 4.75]

B. [1, 3]

C. [2.5, 4.75]

D. []

Solution

1. Step 1: Understand Number.isInteger usage

   The filter keeps only values where Number.isInteger(v) returns true, i.e., whole numbers.

2. Step 2: Apply filter to array

   From [1, 2.5, 3, 4.75], only 1 and 3 are integers, so the filtered array is [1, 3].

3. Final Answer:

   [1, 3] -> Option B

4. Quick Check:

   Filter integers only = [1, 3] [OK]

Hint: Use Number.isInteger to filter whole numbers [OK]

Common Mistakes:

• Expecting decimals to pass Number.isInteger
• Confusing filter output with original array
• Using isInteger incorrectly as a method on numbers