Golang Study Notes - Basic Function Usage and Variable Declaration



  • Printf is an abbreviation for "print formatted"
  • Printf is used to create formatted output
  • Printf does not automatically add a newline character, so you need to add \n or other characters yourself to control line breaks.
  • Printf needs to use placeholders (such as %s, %d, %f, etc.) to specify the format of the output text and provide the corresponding values.


  • Println is an abbreviation for "print line"
  • It is used to print text and add a newline character at the end, with the output content on different lines.
  • Println does not require a formatted string or placeholders.


package main

import "fmt"

func main() {
	name := "Alice"
	age := 30

	// Use Printf for formatted output
	fmt.Printf("Name: %s Age: %d\n", name, age)

	// Use Println for output
	fmt.Println("Name:", name, "Age:", age)

// Output
// Name: Alice Age: 30
// Name: Alice Age: 30


In exported names, the first letter needs to be capitalized. In other words, if a name starts with a capital letter, it is exported.

For example,
fmt.Printf is allowed
fmt.printf is not allowed (Printf needs to be capitalized)


import (

func main() {
	fmt.Println(math.Pi) // Both math.Pi and fmt.Println need to be capitalized

Example of using a function:

package main

import "fmt"

func main() {
	a := 3
	b := 5
	// Use Println to output data
	fmt.Println("a is", a, "sum is", sum(a, b))
	// Use Printf to output data
	fmt.Printf("a is %d , sum is %d", a, sum(a, b))

// Return a value (sum) by specifying a single return parameter type
// func function_name(input_parameter, input_parameter variable_type) (return_type return_type) {
// Function body
func sum(x, y int) int {
	return x + y

Variable Declaration#

Use a := "azusa" to quickly declare a variable a with a value of type string. You do not need to manually set the variable type (note that string types need quotation marks). := structure cannot be used outside of a function.

a := "azusa"
b := 123

is equivalent to

var a string = "azusa"
var b int = 123

More examples:

var i, j int = 1, 2
var c, p, j = true, false, "no!"
// c and p are of type bool, j is of type string

var will also automatically determine the variable type.

Variable declarations without an explicit initial value are assigned their zero value.#

The zero values are:
numeric types are 0,
boolean types are false,
strings are "" (empty string).


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