Dart: Working with numbers

This article is part of a series on How to start creating mobile applications for Android or iOS using Dart & Flutter.

Photo by Mika Baumeister on Unsplash

Addition

When adding two numbers of the same type, the resulting type will be the same. When adding an integer type number to a double type number, the resulting type will be double.

int x = 3;
int y = 4;
var c = x + y; // Result is 7 and result type is int
x += y; // This is equal x = x + y;

double f = 2.3;
double g = 3.0;
var s = f + g; // Result is 5.3 and result type is double

int k = 2;
double t = 2.0;
var y = k + t; // Result is 4.0 and result type is double

Subtraction

When subtracting two numbers of the same type, the resulting type will be the same. When subtracting where one number is of type int and the other number is of type double, the resulting type will be double.

int x = 3;
int y = 4;
var c = x - y; // Result is -1 and result type is int
x -= y; // This is equal x = x - y;

double f = 5.2;
double g = 3.0;
var s = f - g; // Result is 2.2 and result type is double

int k = 4;
double t = 2.0;
var y = k - t; // Result is 2.0 and result type is double
var h= t - k; // Result is -2.0 and result type is double

Multiplication

When multiplying two numbers of the same type, the resulting type will be the same. When multiplying where one number is of type int and the other number is of type double, the resulting type will be double.

int x = 3;
int y = 4;
var c = x * y; // Result is 12 and result type is int
x *= y; // This is equal x = x * y;

double f = 5.2;
double g = 3.0;
var s = f * g; // Result is 15.6 and result type is double

int k = 4;
double t = 2.0;
var y = k * t; // Result is 8.0 and result type is double

Division

When performing a division operation, the resulting type will be double.

int x = 8;
int y = 2;
var c = x / y; // Result is 4 and result type is double

double g = 4.0;
int j = 2;
g /= j; // This is equal g = g / j;

Integer division

The result of integer division will always be of type int.

double x = 11.4;
int y = 2;  
var c = x ~/y; // Result is 5 and result type is int

int d = 5;
double s = 1.3;
d ~/= s; // This is equal d = d ~/ s; and result value is 3

Remainder of integer division

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In this operation, if one of the numbers has the type double, the result will also have the type double.

int x = 11;
double y = 2.3;
var c = 11 % y; // Result is 1.8 and result type is double

double d = 11.0;
double f = 3.3;
d %= f; // This is equal d = d % f; and result value is 1.1

Postfix increment/decrement

The operator is placed after the variable. It first returns the current value of the variable and then changes it.

int x = 10;
print(x++); // It will output 10, then increment x by 1

int y = 20;
print(y--); // It will output 20, then decrement y by 1

print(x); // Now x is equal to 11
print(y); // Now y is equal to 19

Prefix increment/decrement

The operator is placed before the variable. It first changes the value of the variable and then returns the new value.

int a = 7;
print(++a); // It will increment a by 1 and output 8

int b = 12;
print(--b); // It will decrement b by 1 and output 11

print(a); // Now a is equal to 8
print(b); // Now b is equal to 11

The order of arithmetic operations

The order of arithmetic operations in the Dart language is determined by the standard rules of mathematics. The operations are executed in the following order:

1. The unary minus (-) is applied directly to a number, changing its sign.
2. Multiplication (*) and division (/) are performed from left to right.
3. Addition (+) and subtraction (-) are performed from left to right.

You can use parentheses “()” to explicitly specify the order of operations if you want to change the standard order.

int result1 = 5 + 3 * 2;      // First multiplication, then addition: 11
int result2 = (5 + 3) * 2;    // First parentheses, then multiplication: 16

double result3 = 10 / 2 + 3;   // First division, then addition: 8.0
double result4 = 10 / (2 + 3); // First parentheses, then division: 2.0

int result5 = -5 + 8 * 2;     // Unary minus, then multiplication and addition: 11

If there are multiple operations of the same type in an expression (for example, multiple additions or multiplications), they are performed from left to right, regardless of their arrangement.

int result6 = 10 - 2 - 3;  // Subtraction is performed from left to right: 5
int result7 = 2 * 3 * 4;   // Multiplication is performed from left to right: 24

These rules allow you to control the order of arithmetic operations in Dart and ensure accurate calculation results. If you need to modify the order of operations, use parentheses to explicitly specify the priority.