Golang Tutorial 001 Essentials

sudo rm -rf /usr/local/go
brew uninstall go
brew install wget
wget https://golang.org/dl/go1.22.3.darwin-arm64.tar.gz
sudo tar -C /usr/local -xzf go1.22.3.darwin-arm64.tar.gz
source ~/.zshrc  # or source ~/.bash_profile

package main

import (
	"fmt"
	"math"
	"reflect"
)

// interface is like any in typescript
func checkType(value interface{}) {
	var t = reflect.TypeOf(value)
	fmt.Printf("Type from reflect of %v is %v\n", value, t)
}

func main() {
	fmt.Println("Welcome to Golang Tutorial 2024!!!")
	// same as python, your data type can be inferred
	// but you should declare your data type explicitly
	// basic data types
	var aBool bool = true
	var anInteger int64 = 123
	var aFloat float64 = 1.23

	checkType(aBool)
	checkType(anInteger)
	checkType(aFloat)

	// calculation
	a, b := 3, 4 // short hand for inferred type declaration
	var c = math.Sqrt(math.Pow(float64(a), 2) + math.Pow(float64(b), 2))
	checkType(c)
	// i^2 = -1
	// z = a + bi
	// eg: (x+1)^2 = -9
	// x = -1 + 3i || x = -1 - 3i
	var aComplexNumber = -1 + 3i
	var calculationOfComplexNumber = (aComplexNumber + 1) * (aComplexNumber + 1)
	checkType(aComplexNumber)
	checkType(calculationOfComplexNumber)

	// string is a sequence of bytes
	var aString = "abcdef"
	checkType(aString)

	var aRune = 'a'
	checkType(aRune)

	// constant
	const PI = 3.14
	const circleRadius = 5
	var circleCircumFerence = PI * circleRadius
	checkType(circleCircumFerence)

	// pointer
	var number int = 0
	fmt.Print("Please enter random number: ")
	fmt.Scan(&number)
	if number > 0 {
		fmt.Printf("Your number %v is greater than 0", number)
	} else {
		fmt.Printf("Your number %v is less than 0", number)
	}

	// some special types: byte(int8), rune(int32 - a Unicode code point), any(interface{}), nil

	// composites
}

// A = P*(1+r/n)^n*t
// A : compound interest
// P : investment value
// r : interest rate
// n : compound (continuously, monthly,quarterly,annually)
// t : investment times in years
func calculateCompoundInterest() {
	var investmentValueP int64
	var interestRateR float64
	var compound int8
	var compoundN int8
	var investmentTimesT int8
	fmt.Print("Please enter your investment value: ")
	fmt.Scan(&investmentValueP)
	fmt.Print("Please enter your interest rate: ")
	fmt.Scan(&interestRateR)
	fmt.Print("Please enter your compound terms \n1. Monthly\n2. Quarterly\n3.Annually\nYour selection is : ")
	fmt.Scan(&compound)
	const MONTHLY = 1
	const QUARTERLY = 2
	switch compound {
	// monthly
	case MONTHLY:
		compoundN = 12
	case QUARTERLY:
		compoundN = 4
	default: // yearly or other type
		compoundN = 1
	}
	fmt.Print("How many years are you planning to invest: ")
	fmt.Scan(&investmentTimesT)
	fmt.Println("Please wait while system is calculating ...")
	var compoundInterestA = float64(investmentValueP) * math.Pow((1+interestRateR/100/float64(compoundN)), float64(compoundN*investmentTimesT))
	var interestValueI = compoundInterestA - float64(investmentValueP)
	fmt.Printf("After %v %v of investing.\nYour principle amount go from %v to %v.\nYour interest value is %v", investmentTimesT, compoundN, investmentValueP, compoundInterestA, interestValueI)
}

// explicit return
func sum(a int, b int) int {
	return a + b
}

// implicit return
func multiple(a int, b int) (z int) {
	z = a * b
	return
}

func theATMApplication() {
	var balance uint64 = 10000
	const pinCode uint64 = 123456
	const ACT_CHECK_BALANCE = 1
	const ACT_WITHDRAW = 2
	const ACT_TRANFERS = 3
	const ACT_EXIT = 4
	const WRONG_PIN_LIMIT = 5
	var numberOfTries int8 = 0
	fmt.Println("Welcome to our ATM")

	// check pinCode, if user enter pinCode wrong 5 times, block their card
	for {
		var inputPinCode uint64
		fmt.Print("Please enter your pin: ")
		fmt.Scan(&inputPinCode)
		if inputPinCode != pinCode {
			numberOfTries += 1
			if numberOfTries < WRONG_PIN_LIMIT {
				fmt.Println("In correct pin, please try again")
				continue
			} else {
				// otherwise, block their card, and stop the program
				fmt.Printf("You have been enter wrong pin for %v times\n", WRONG_PIN_LIMIT)
				fmt.Print("We will lock your card, please go to your bank branch for support!\n")
				return
			}
		}
		// if no error
		break
	}
	// if user already pass the authorization, process next step
	for {
		options := ""
		options += fmt.Sprintf("\n1. Check balance\n")
		options += fmt.Sprintf("2. Withdraw\n")
		options += fmt.Sprintf("3. Transfer\n")
		options += fmt.Sprintf("4. Exit\n")
		fmt.Println(options)
		var choice int8
		fmt.Print("Please select your choice: ")
		fmt.Scan(&choice)
		if choice == ACT_EXIT {
			break
		}
		if choice == ACT_CHECK_BALANCE {
			checkBalance(balance)
			continue
		}
		if choice == ACT_WITHDRAW {
			var withdrawNumber uint64
			fmt.Print("Please enter your withdraw amount: ")
			fmt.Scan(&withdrawNumber)
			if withdrawNumber > balance {
				fmt.Println("Invalid amount, you can not withdraw more than you have!")
				continue
			}
			// if it is okie
			balance = balance - withdrawNumber
			fmt.Printf("Balance updated! New amount: %v\n", balance)
			continue
		}
		break
	}
	fmt.Println("Thank you for using our service!")
}

func checkBalance(balance uint64) {
	fmt.Printf("Your balance is %v\n", balance)
}