# Go operators

In this tutorial we cover Go operators. We show how to use operators to create expressions.

An operator is a special symbol which indicates a certain process is carried out. Operators in programming languages are taken from mathematics. Programmers work with data. The operators are used to process data. An operand is one of the inputs (arguments) of an operator.

Expressions are constructed from operands and operators. The operators of an expression indicate which operations to apply to the operands. The order of evaluation of operators in an expression is determined by the precedence and associativity of the operators.

An operator usually has one or two operands. Those operators that work with only one operand are called unary operators. Those who work with two operands are called binary operators.

Certain operators may be used in different contexts. For instance the `+` operator can be used in different cases: it adds numbers, concatenates strings, or indicates the sign of a number. We say that the operator is overloaded.

## Go sign operators

There are two sign operators: `+` and `-`. They are used to indicate or change the sign of a value.

sign_operators.go
```package main

import "fmt"

func main() {

fmt.Println(2)
fmt.Println(+2)
fmt.Println(-2)
}
```

The `+` and `-` signs indicate the sign of a value. The plus sign can be used to signal that we have a positive number. It can be omitted and it is in most cases done so.

minus_sign.go
```package main

import "fmt"

func main() {

var a = 1

fmt.Println(-a)
fmt.Println(-(-a))
}
```

The minus sign changes the sign of a value.

## Go assignment operator

The assignment operator `=` assigns a value to a variable. A variable is a placeholder for a value. In mathematics, the = operator has a different meaning. In an equation, the `=` operator is an equality operator. The left side of the equation is equal to the right one.

```var x = 1
```

Here we assign a number to the `x` variable.

```x = x + 1
```

This expression does not make sense in mathematics, but it is legal in programming. The expression adds 1 to the `x` variable. The right side is equal to 2 and 2 is assigned to `x`.

```3 = x
```

This code line leads to a syntax error. We cannot assign a value to a literal.

```x := 2
```

Go has a short variable declaration operator `:=`; it declares a variable and assigns a value in one step. The `x := 2` is equal to `var x = 2`.

### Go increment and decrement operators

We often increment or decrement a value by one in programming. Go has two convenient operators for this: `++` and `--`.

```x++ //  x = x + 1
y-- // y = y - 1
```
inc_dec.go
```package main

import "fmt"

func main() {

x := 6

x++
x++

fmt.Println(x)

x--
fmt.Println(x)
}
```

In the above example, we demonstrate the usage of both operators.

```x := 6

x++
x++
```

We initiate the `x` variable to 6. Then we increment `x` two times. Now the variable equals to 8.

```x--
```

We use the decrement operator. Now the variable equals to 7.

```\$ go run inc_dec.go
8
7
```

## Go compound assignment operators

The compound assignment operators consist of two operators. They are shorthand operators.

```a = a + 3
a += 3
```

The `+=` compound operator is one of these shorthand operators. The above two expressions are equal. Value 3 is added to the a variable.

Other compound operators include:

````-=   *=   /=   %=   &=   |=   <<=   >>=`
```
compound_operators.go
```package main

import "fmt"

func main() {

var a int = 1
a = a + 1

fmt.Println(a)

a += 5
fmt.Println(a)

a *= 3
fmt.Println(a)
}
```

In the example, we use two compound operators.

```var a int = 1
a = a + 1
```

The `a` variable is initiated to one. 1 is added to the variable using the non-shorthand notation.

```a += 5
```

Using a `+=` compound operator, we add 5 to the `a` variable. The statement is equal to `a = a + 5`.

```a *= 3
```

Using the `*=` operator, the `a` is multiplied by 3. The statement is equal to `a = a * 3`.

```\$ go run compound_operators.go
2
7
21
```

## Go arithmetic operators

The following is a table of arithmetic operators in Go.

SymbolName
`+`Addition
`-`Subtraction
`*`Multiplication
/Division
`%`Remainder

The following example shows arithmetic operations.

arithmetic.go
```package main

import "fmt"

func main() {

var a = 10
var b = 11
var c = 12

var add = a + b + c
var sb = c - a
var mult = a * b
var div = c / 3
var rem = c % a

fmt.Println(sb)
fmt.Println(mult)
fmt.Println(div)
fmt.Println(rem)
}
```

In the preceding example, we use addition, subtraction, multiplication, division, and remainder operations. This is all familiar from the mathematics.

```var rem = c % a
```

The `%` operator is called the remainder or the modulo operator. It finds the remainder of division of one number by another. For example, `9 % 4`, 9 modulo 4 is 1, because 4 goes into 9 twice with a remainder of 1.

```\$ go run arithmetic.go
33
2
110
4
2
```

Next we will show the distinction between integer and floating point division.

division.go
```package main

import "fmt"

func main() {

c := 5 / 2
fmt.Println(c)

d := 5 / 2.0
fmt.Println(d)
}
```

In the preceding example, we divide two numbers.

```c := 5 / 2
fmt.Println(c)
```

In this code, we have done integer division. The returned value of the division operation is an integer. When we divide two integers the result is an integer.

```d := 5 / 2.0
fmt.Println(d)
```

If one of the values is a double or a float, we perform a floating point division. In our case, the second operand is a double so the result is a double.

```\$ go run division.go
2
2.5
```

## Go Boolean operators

In Go we have three logical operators.

SymbolName
`&&`logical and
`||`logical or
`!`negation

Boolean operators are also called logical.

boolean_exp.go
```package main

import "fmt"

func main() {

var x = 3
var y = 8

fmt.Println(x == y)
fmt.Println(y > x)

if y > x {

fmt.Println("y is greater than x")
}
}
```

Many expressions result in a boolean value. For instance, boolean values are used in conditional statements.

```fmt.Println(x == y)
fmt.Println(y > x)
```

Relational operators always result in a boolean value. These two lines print false and true.

```if y > x {

fmt.Println("y is greater than x")
}
```

The body of the `if` statement is executed only if the condition inside the parentheses is met. The `y > x` returns true, so the message "y is greater than x" is printed to the terminal.

The `true` and `false` keywords represent boolean literals in Go.

and_operator.go
```package main

import "fmt"

func main() {

var a = true && true
var b = true && false
var c = false && true
var d = false && false

fmt.Println(a)
fmt.Println(b)
fmt.Println(c)
fmt.Println(d)
}
```

The code example shows the logical and (&&) operator. It evaluates to true only if both operands are true.

```\$ go run and_operator.go
true
false
false
false
```

Only one expression results in true.

The logical or (`||`) operator evaluates to true if either of the operands is true.

or_operator.go
```package main

import "fmt"

func main() {

var a = true || true
var b = true || false
var c = false || true
var d = false || false

fmt.Println(a)
fmt.Println(b)
fmt.Println(c)
fmt.Println(d)
}
```

If one of the sides of the operator is true, the outcome of the operation is true.

```\$ go run or_operator.go
true
true
true
false
```

Three of four expressions result in true.

The negation operator `!` makes true false and false true.

negation_operator.go
```package main

import "fmt"

func main() {

fmt.Println(!true)
fmt.Println(!false)
fmt.Println(!(4 < 3))
}
```

The example shows the negation operator in action.

```\$ go run negation_operator.go
false
true
true
```

## Go comparison operators

Comparison operators are used to compare values. These operators always result in a boolean value.

SymbolMeaning
`<`less than
`<=`less than or equal to
`>`greater than
`>=`greater than or equal to
`==`equal to
`!=`not equal to

comparison operators are also called relational operators.

comparison_operators.go
```package main

import "fmt"

func main() {

fmt.Println(3 < 4)
fmt.Println(3 == 4)
fmt.Println(4 >= 3)
fmt.Println(4 != 3)
}
```

In the code example, we have four expressions. These expressions compare integer values. The result of each of the expressions is either true or false. In Go we use the `==` to compare numbers. (Some languages like Ada, Visual Basic, or Pascal use `=` for comparing numbers.)

## Go bitwise operators

Decimal numbers are natural to humans. Binary numbers are native to computers. Binary, octal, decimal, or hexadecimal symbols are only notations of the same number. Bitwise operators work with bits of a binary number.

SymbolMeaning
`^`bitwise exclusive or
`&`bitwise and
`|`bitwise or
`&^`bit clear (and not)
`<<`left shift
`>>`right shift

The bitwise and operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 only if both corresponding bits in the operands are 1.

```      00110
&  00011
=  00010
```

The first number is a binary notation of 6, the second is 3, and the result is 2.

```fmt.Println(6 & 3) // prints 2
fmt.Println(3 & 6) // prints 2
```

The bitwise or operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 if either of the corresponding bits in the operands is 1.

```     00110
| 00011
= 00111
```

The result is `00110` or decimal 7.

```fmt.Println(6 | 3) // prints 7
fmt.Println(3 | 6) // prints 7
```

The bitwise exclusive or operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 if one or the other (but not both) of the corresponding bits in the operands is 1.

```      00110
^  00011
=  00101
```

The result is `00101` or decimal 5.

```fmt.Println(6 ^ 3) // prints 5
fmt.Println(3 ^ 6) // prints 5
```

## Go pointer operators

In Go, the `&` is an address of operator and the `*` is a pointer indirection operator.

pointer_op.go
```package main

import "fmt"

func main() {

var count int = 4
fmt.Println(count)

var pv = &count
*pv = 3
fmt.Println(pv)
fmt.Println(*pv)
}
```

In the example, we demonstrate the two operators.

```var count int = 4
```

An integer variable is defined.

```var pv = &count
```

We get the address of the `count` variable; we create a pointer to the variable.

```*pv = 3
```

Via the pointer dereference, we modify the value of count.

```fmt.Println(*pv)
```

Again, via pointer dereference, we print the value to which the pointer refers.

```\$ go run pointer_op.go
4
0xc0000140f8
3
```

## Go channel operator

A channels is a typed conduit through which we can send and receive values with the channel operator `<-`.

channel_op.go
```package main

import "fmt"

func main() {

messages := make(chan string)

go func() { messages <- "hello" }()

msg := <-messages
fmt.Println(msg)
}
```

The example presents the channel operator.

```go func() { messages <- "hello" }()
```

We send a value to the channel.

```msg := <-messages
```

We receive a value from the channel.

## Go operator precedence

The operator precedence tells us which operators are evaluated first. The precedence level is necessary to avoid ambiguity in expressions.

What is the outcome of the following expression, 28 or 40?

```3 + 5 * 5
```

Like in mathematics, the multiplication operator has a higher precedence than addition operator. So the outcome is 28.

```(3 + 5) * 5
```

To change the order of evaluation, we can use parentheses. Expressions inside parentheses are always evaluated first. The result of the above expression is 40.

operator_precedence.go
```package main

import "fmt"

func main() {

fmt.Println(3 + 5*5)
fmt.Println((3 + 5) * 5)

fmt.Println(!true || true)
fmt.Println(!(true || true))
}
```

In this code example, we show a few expressions. The outcome of each expression is dependent on the precedence level.

```fmt.Println(3 + 5*5)
```

This line prints 28. The multiplication operator has a higher precedence than addition. First, the product of `5 * 5` is calculated, then 3 is added.

```fmt.Println((3 + 5) * 5)
```

The evaluation of the expression can be altered by using round brackets. In this case, the `3 + 5` is evaluated and later the value is multiplied by 5. This line prints 40.

```fmt.Println(!true || true)
```

In this case, the negation operator has a higher precedence than the bitwise or. First, the initial true value is negated to false, then the `|` operator combines false and true, which gives true in the end.

```\$ go run precedence.go
28
40
true
false
```

## Associativity rule

Sometimes the precedence is not satisfactory to determine the outcome of an expression. There is another rule called associativity. The associativity of operators determines the order of evaluation of operators with the same precedence level.

```9 / 3 * 3
```

What is the outcome of this expression, 9 or 1? The multiplication, deletion, and the modulo operator are left to right associated. So the expression is evaluated this way: `(9 / 3) * 3` and the result is 9.

Arithmetic, boolean and relational operators are left to right associated. The ternary operator, increment, decrement, unary plus and minus, negation, bitwise not, type cast, object creation operators are right to left associated.

associativity.go
```package main

import "fmt"

func main() {

var j = 0

j *= 3 + 1

fmt.Println(j)
}
```

In the example, we the associativity rule determines the outcome of the expression.

```var j = 0

j *= 3 + 1
```

The compound assignment operators are right to left associated. We might expect the result to be 1. But the actual result is 0. Because of the associativity. The expression on the right is evaluated first and then the compound assignment operator is applied.

In this tutorial, we have covered Go operators.

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