Data Types

Welcome to tutorial number 4 in our Golang tutorial series.

Please read Golang tutorial part 3: Variables of this series to learn about variables.

The following are the basic data types available in Go

• bool
• Numeric Types
  • int8, int16, int32, int64, int
  • uint8, uint16, uint32, uint64, uint
  • float32, float64
  • complex64, complex128
  • byte
  • rune
• string

bool

bool type represents a boolean. It can either be a true or false value.

 1package main
 2
 3import "fmt"
 4
 5func main() {
 6	a := true
 7	b := false
 8	fmt.Println("a:", a, "b:", b)
 9	c := a && b
10	fmt.Println("c:", c)
11	d := a || b
12	fmt.Println("d:", d)
13}

Run in playground

In the program above, a is assigned to true and b is assigned a false value.

&& is a boolean operator which returns true when both of the operands are true.

c is assigned the value of a && b. In this case c is false since both a and b are not true.

The || operator returns true when either a or b is true. In this case d is true since a is true. We will get the following output for this program.

a: true b: false
c: false
d: true

Signed integers

The following are the signed integer data types available in Go.

1package main
2
3import "fmt"
4
5func main() {
6	var a int = 89
7	b := 95
8	fmt.Println("value of a is", a, "and b is", b)
9}

Run in playground

The above program will print

value of a is 89 and b is 95

In the above program a is of type int and the type of b is inferred from the value assigned to it (95). As we have stated above, the size of int is 32 bit in 32 bit systems and 64 bit in 64 bit systems. Let’s go ahead and verify this claim.

The type of a variable can be printed using %T format specifier in Printf function. Go has a unsafe package which has a Sizeof function which returns the size of the variable in bytes. unsafe package should be used with care as the code using it might have portability issues, but for the purposes of this tutorial we can use it.

The following program outputs the type and size of both variables a and b. %T is the format specifier to print the type and %d is used to print the size.

 1package main
 2
 3import (
 4	"fmt"
 5
 6	"unsafe"
 7)
 8
 9func main() {
10
11	var a = 89
12	b := 95
13	fmt.Println("value of a is", a, "and b is", b)
14	fmt.Printf("type of a is %T, size of a is %d bytes", a, unsafe.Sizeof(a))   //type and size of a
15	fmt.Printf("\ntype of b is %T, size of b is %d bytes", b, unsafe.Sizeof(b)) //type and size of b
16}

Run in playground

The above program will print the following output

value of a is 89 and b is 95
type of a is int, size of a is 8 bytes
type of b is int, size of b is 8 bytes

We can infer from the above output that a and b are of type int and they have a size of 8 bytes(64 bits). The output will vary if you run the above program on a 32 bit system. In a 32 bit system, a and b occupy 4 bytes(32 bits).

Unsigned integers

The Unsigned integer type as the name indicates can only be used to store positive integers. The following are the unsigned integer data types available in Go.

Unsigned integers are used in places where negative values are not applicable.

In the following program, the variables a and b are of type uint.

 1package main
 2
 3import "fmt"
 4
 5func main() {
 6	var a uint = 60
 7	var b uint = 30
 8	c := a * b
 9	fmt.Println("c =", c)
10	fmt.Printf("Data type of variable c is %T", c)
11}

Run in playground

The above program prints

1c = 1800
2Data type of variable c is uint

Since a and b are both of type uint, the inferred type of c is also uint

Floating point types

The following is a simple program to illustrate integer and floating point types

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	a, b := 5.67, 8.97
 9	fmt.Printf("type of a %T b %T\n", a, b)
10	sum := a + b
11	diff := a - b
12	fmt.Println("sum of %d and %d is", sum, ", diff", diff)
13
14	no1, no2 := 56, 89
15	fmt.Println("sum of %d and %d is", no1+no2, ", diff", no1-no2)
16}

Run in playground

The type of a and b is inferred from the value assigned to them. In this case a and b are of type float64. float64 is the default type for floating point values. We add a and b and assign it to a variable sum. We subtract b from a and assign it to diff. Then sum and diff are printed. Similar computation is done with no1 and no2. The above program will print,

type of a float64 b float64
sum of 5.670000 and 8.970000 is 14.640000, diff is -3.300000
type of no1 int no2 int
sum of 56 and 89 is 145, diff is -33

Complex types

The standard library function complex is used to construct a complex number with real and imaginary parts. The complex function has the following definition

func complex(r, i FloatType) ComplexType

It takes a real and imaginary part as a parameter and returns a complex type. Both the real and imaginary parts must be of the same type. ie either float32 or float64. If both the real and imaginary parts are float32, this function returns a complex value of type complex64. If both the real and imaginary parts are of type float64, this function returns a complex value of type complex128

Complex numbers can also be created using the shorthand syntax

c := 6 + 7i

Let’s write a small program to understand complex numbers.

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	c1 := complex(5, 7)
 9	c2 := 8 + 27i
10	cadd := c1 + c2
11	fmt.Println("sum:", cadd)
12	cmul := c1 * c2
13	fmt.Println("product:", cmul)
14}

Run in playground

In the above program, c1 and c2 are two complex numbers. c1 has 5 as real part and 7 as the imaginary part. c2 has real part 8 and imaginary part 27. cadd is assigned the sum of c1 and c2 and cmul is assigned the product of c1 and c2. This program will output

sum: (13+34i)
product: (-149+191i)

Other numeric types

byte is an alias of uint8
rune is an alias of int32

We will discuss bytes and runes in more detail when we learn about strings.

string type

Strings are a collection of bytes in Go. It’s alright if this definition doesn’t make any sense. For now, we can assume a string to be a collection of characters. We will learn about strings in detail in a separate strings tutorial.

Let’s write a program using strings.

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	first := "Naveen"
 9	last := "Ramanathan"
10	name := first +" "+ last
11	fmt.Println("My name is",name)
12}

Run in playground

In the above program, first is assigned the string Naveen, last is assigned the string Ramanathan. Strings can be concatenated using the + operator. name is assigned the value of first concatenated by a space followed by last. The above program will print

1My name is Naveen Ramanathan

as the output.

There are some more operations that can be performed on strings. We will look at those in a separate tutorial.

Type Conversion

Go is very strict about explicit typing. There is no automatic type promotion or conversion. Let’s look at what this means with an example.

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	a := 80      //int
 9	b := 91.8    //float64
10	sum := a + b //int + float64 not allowed
11	fmt.Println(sum)
12}

Run in playground

The above code is perfectly legal in C language, but in Go this program won’t compile. a is of type int and b is float64. We are trying to add 2 numbers of different types which is not allowed. When you run the program, you will get the following compilation error

1./prog.go:10:9: invalid operation: a + b (mismatched types int and float64)

To fix the error, both a and b must be of the same type. Let’s convert b to int. T(v) is the syntax to convert a value v to type T

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	a := 80           //int
 9	b := 91.8         //float64
10	sum := a + int(b) //int + float64 not allowed
11	fmt.Println(sum)
12}

Run in playground

Since b is converted from float to int, its floating point will be truncated and hence we see 171 as the output.

The same is the case with assignment. Explicit type conversion is required to assign a variable of one type to another. This is explained in the following program.

 1package main
 2
 3import (
 4	"fmt"
 5)
 6
 7func main() {
 8	i := 10
 9	var j float64 = float64(i) //this statement will not work without explicit conversion
10	fmt.Println("j =", j)
11}

Run in playground

In line no. 9, i is converted to float64 and then assigned to j. When you try to assign i to j without any type conversion, the compiler will throw an error.

This brings us to an end of this tutorial. Please post your feedback and queries in the comments section. Please consider sharing this tutorial on twitter or LinkedIn. Have a good day.

Next Tutorial - Constants

Previous Tutorial - Variables