[Golang 03/30] Go: data types commonly used

Numeric Types:

• int: Signed integer type.
• int8, int16, int32, int64: Signed integer types with specific bit sizes.
• uint: Unsigned integer type.
• uint8, uint16, uint32, uint64: Unsigned integer types with specific bit sizes.
• float32, float64: Floating-point types for representing decimal numbers.
• complex64, complex128: Complex number types for representing real and imaginary parts.

Positive and negative integer

int depends on the running system. If you're running Go on 32-bit OS system, the default type for int is int32， and its range is -2^31 to 2^31-1(-2147483648, 2147483647)

Positive integer

unit8 has the range of (0, 2^8-1), i.e. (0, 255)

Boolean Type:

bool: Represents a Boolean value (true or false).

String Type:

string: Represents a sequence of characters.

Array Types:

array: A fixed-size collection of elements of the same type. The size of an array is determined at compile-time.

Slice Type:

slice: A flexible, dynamically-sized sequence of elements. Slices are built on top of arrays.

package main

import (
    "fmt"
)

func main() {
    var intA int = -12
    fmt.Printf("\nintA: %d", intA)
    //intA: -12

    var intB uint = 12
    fmt.Printf("\nintB: %d", intB)
    //intB: 12

    var floatA float64 = 98.6
    fmt.Printf("\nfloatA: %f", floatA)
    //floatA: 98.600000

    var stringVar string = "hello world!"
    fmt.Printf("\nstringVar: %s", stringVar)
    // stringVar: hello world!

    var boolVar bool = true
    fmt.Printf("\nboolVar: %t\n", boolVar)
    // boolVar: true

    var numbers = []int{0, 1, 2, 3, 4, 5}
    fmt.Printf("Size of 'numbers' is %d\n", len(numbers))
    fmt.Println(numbers)
    // Size of 'numbers' is 6
    // [0 1 2 3 4 5]

    numbers = append(numbers, 6, 7)
    fmt.Printf("Size of 'numbers' is changed to %d\n", len(numbers))
    fmt.Println(numbers)
    // Size of 'numbers' is changed to 8
    // [0 1 2 3 4 5 6 7]

    sliced := numbers[1:5]
    fmt.Printf("sliced numbers: ")
    fmt.Println(sliced)
    // sliced numbers: [1 2 3 4]

    numberArray := [3]int{1, 2}
    fmt.Printf("numberArray with size 3 and default value:")
    fmt.Println(numberArray)
    // numberArray with size 3 and default value:[1 2 0]


}

Map Type:

map: An unordered collection of key-value pairs, where each key is unique.

package main

import "fmt"

func main() {
    // Create a map to store employee names and their corresponding IDs
    // key: string, value: int
    employees := make(map[string]int)
    fmt.Printf("current size of this map: %d\n", len(employees))
    // current size of this map: 0

    // Add key-value pairs to the map
    employees["John"] = 1001
    employees["Alice"] = 1002
    employees["Bob"] = 1003
    fmt.Println(employees)
    // map[Alice:1002 Bob:1003 John:1001]

    // Accessing values from the map
    fmt.Println(employees["Alice"])  
    // Output: 1002

    // Modifying values in the map
    employees["Bob"] = 1004

    // Deleting a key-value pair from the map
    delete(employees, "John")

    // Print the updated map
    fmt.Println(employees)
    // map[Alice:1002 Bob:1004]

    // Checking if a key exists in the map
    id, exists := employees["Alice"]
    if exists {
        fmt.Println("Alice's ID:", id)
        // Alice's ID: 1002
    } else {
        fmt.Println("Alice not found")
    }

    var keys []string
    for key :=range employees {
      keys = append(keys, key)
    }
    fmt.Printf("Keys from the map 'employees': ")
    fmt.Println(keys)
    // Keys from the map 'employees': [Alice Bob]
}