Beginner 20 min read

Numbers

By the end of this lesson, you'll be able to:

Choose the correct numeric type (Integer, Decimal, Long, Double) for a given value
Perform basic arithmetic with numeric variables
Explain why Decimal is generally preferred over Double for money

Prerequisites: "What Is a Variable?"

The four numeric types

Type	Holds	Typical use
`Integer`	Whole numbers, up to about 2.1 billion	Counts, ages, quantities
`Long`	Whole numbers, much larger than Integer	Very large IDs or counts
`Decimal`	Fixed-precision fractional numbers	Money, always
`Double`	Floating-point fractional numbers	Scientific/approximate values

A real business example: Banking

Decimal accountBalance = 1042.55;
Integer numberOfTransactions = 12;

accountBalance is a Decimal, never a Double — banking math needs exact precision, and Double can introduce tiny rounding errors from how computers represent fractional numbers internally. numberOfTransactions is a whole count, so Integer fits naturally.

Common mistakes

Using Double for money. This is the single most common numeric mistake in Apex — Double rounding errors can silently produce financial figures that are off by fractions of a cent, which compounds into real, confusing bugs.
Assuming Integer division gives a fractional result. 7 / 2 using two Integers gives 3, not 3.5 — division truncates unless at least one operand is a Decimal or Double.

Integer division truncates

Integer result = 7 / 2;
System.debug(result);          // 3, not 3.5

Decimal preciseResult = 7.0 / 2;
System.debug(preciseResult);   // 3.5

Integer division discards the remainder entirely. Making either operand a Decimal (7.0 instead of 7) forces Apex to do fractional division instead.

Exercise

Declare a Decimal called pricePerUnit (12.50) and an Integer called quantity (4). Calculate and debug the total cost.

Show hint

Decimal * Integer works fine in Apex — the result comes out as a Decimal.

APEX

Numbers Quiz

1. Which numeric type should you use for money?

Decimal Double Long It does not matter

2. Dividing two Integers in Apex always produces a whole number result (the remainder is discarded).

True False

My Notes

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Summary

Apex has four numeric types — Integer for whole numbers, Decimal for precise fractional values (like money), Long for very large whole numbers, and Double for less-precise fractional values — and picking the right one matters more than it might first appear.

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