Go (Golang) Tutorial 4 - Print Formatting and Input

In this tutorial, we will learn about the fmt package. By the end of this tutorial, you’ll have a solid understanding of the fmt package covering everything from printing, formatting data, and reading input.

Printing data

We have already seen how to use the Println method. One alternative method is called Print.

fmt.Print("Hello!")
fmt.Print("Go is awesome")

This will not insert any new line and both print statements will end up on the same line. If we would like to add a newline we have 2 options.

We can use the escape key \n and it will add a new line.

fmt.Print("Hello!\n")
fmt.Print("Go is awesome")

We could also replace it by using Println and the result will be the same

fmt.Println("Hello!")
fmt.Println("Go is awesome")

It’s possible to pass multiple values to the print statement and it will output all of them.fmt

fmt.Print("My name is", "Patrik")

We can also output variables to the console

name := "Patrik"
lang := "Go"

fmt.Println("My name is", name)
fmt.Println("I love the" + lang + " programming language")

Formatting data

Printf & Sprintf

In Go we can also use something called formatting. It simplifies inserting variables into text, making the code more readable and easier to manage.

To format data We can use the Printf method.

name := "Patrik"
countBurgers := 2

fmt.Printf("My name is %s and I had %d burgers today!", name, age)

%s and %d are placeholders inserted into strings and indicate the type of data and its display format.

There is also an alternative method called Sprintf instead of priting the formatted string it will return it.

name := "Patrik"
countBurgers := 2

sentence := fmt.Sprintf("My name is %s and I had %d burgers today!", name, age)

fmt.Println(sentence)

Format Specifiers

Here are the different Format Specifiers grouped by type that can be used when formatting data.

General

%v Default format for the variable
%#v A Go-syntax representation of the value
%T Prints the type of the value

Boolean

%t Boolean (true or false)

Integer

%d Decimal integer
%b Binary integer
%o Octal integer
%x Hexadecimal integer (lowercase letters)
%X Hexadecimal integer (uppercase letters)
%c The character represented by the corresponding Unicode code point
%q A single-quoted character literal safely escaped with Go syntax.

Floating-Point and Complex Numbers

%f Decimal floating point, no exponent
%b Scientific notation (with binary exponent), e.g., -123456p-78
%e Scientific notation, e.g., -1.234456e+78
%E Scientific notation, e.g., -1.234456E+78
%g Compact representation (chooses %e or %f automatically)
%G Compact representation (chooses %E or %F automatically)

String and Slices

%s String or slice of bytes
%q A double-quoted string safely escaped with Go syntax
%x Base 16, lowercase letters, two characters per byte of the argument
%X Base 16, uppercase letters, two characters per byte of the argument

Pointer

%p Pointer address

Width and Precision

%.2f Floating point with 2 digits after the decimal point
%9f Floating point with 9 characters width
%9.2f Width of 9 and precision of 2
%9s String with a minimum width of 9 characters, right-justified by default
%-9s String with a minimum width of 9 characters, left-justified

Padding and Alignment

%05d Integer padded with zeros to a width of 5 digits
% 5d Integer right-aligned in a field of 5 characters wide
%-5s String left-aligned in a field of 5 characters wide

Reading user input

So far we have only been printing data but what if we want to read user input. To do this we can use the Scan method.

var name string
var age int

fmt.Println("Enter your name: ")
fmt.Scan(&name)

fmt.Println("Enter your age: ")
fmt.Scan(&age)

fmt.Printf("Hello, %s! You are %d years old.\n", name, age)

First, we declare two variables. After that, we ask the user to enter their name. Next, we use the Scan method to receive the user input. Notice we put & before the variable, the reason for this is we want to pass the memory address of the variable so the scan method can update that address with the received value. After that, we do the same for the age. As a last step, we print out the values using the Printf method.

You can also scan multiple values with 1 Scanstatement.

var favColor1 string
var favColor2 string


fmt.Println("Enter your two favorite colors: ")
fmt.Scan(&favColor1, &favColor2)

fmt.Println("favorite colors ", favColor1, favColor2)

This reads input values until it encounters spaces or newlines, and it assigns them to favColor1 and favColor2. The function continues to prompt until all specified variables are filled, allowing inputs across multiple lines.

If you want both values to be read from the same line you can use Scanln

var favColor1 string
var favColor2 string


fmt.Println("Enter your two favorite colors: ")
fmt.Scanln(&favColor1, &favColor2)

fmt.Println("favorite colors ", favColor1, favColor2)

It reads all required input from a single line, separated by spaces, and assigns them to the variables in one go.

If we can the input to match a specific format we can use the method Scanf.

var favColor1 string
var favColor2 string

fmt.Println("Enter your two favorite colors separated by a comma (e.g., red,blue): ")

fmt.Scanf("%s,%s", &favColor1, &favColor2)

fmt.Printf("Your favorite colors are: %s and %s.\n", favColor1, favColor2)

We use the fmt.Scanf with %s,%s to tell Go to expect two string inputs separated by a comma. fmt.Printf formats and displays a message with the user’s favorite colors.

Conclusion

Full source code can be found here Github

In this tutorial, we’ve explored how to print, format, and read data in Go using the fmt package. We covered basic printing with fmt.Print and fmt.Println, detailed formatting with fmt.Printf and fmt.Sprintf, and how to capture user input withfmt.Scan, fmt.Scanln, and fmt.Scanf. In the next tutorial, we gonna talk about arrays & slices.