We’ll take a break of the theory an do some exercises. In this sessions you’ll use everything you’ve learned so far to solve some toy problems.
Practice exercises
Worst multiplication algorithm ever
Write a program that multiplies 2 positive integers only using consecutive additions.
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package main
import "fmt"
func main() {
var multiplicand, multiplier, total int = 8, 7, 0
for i := 0; i < multiplier; i++ {
total += multiplicand
}
fmt.Printf("The result of %d * %d is: %d", multiplicand, multiplier, total)
}
Note: Think what will happen with this algorithm when the multiplicand and/or multiplier are negative. How would you solve the problems that arise.
FizzBuzz
Write a program that counts from 0 to n, replacing all numbers divisible by 3 with the word fizz and all numbers
divisible by 5 with the word buzz and, all the numbers divisible by 3 and 5 with the word fizbuzz1.
I’ll show you 3 alternatives to solve this problem:
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// Solution 1
package main
import "fmt"
func main() {
for i := 1; i <= 100; i++ {
if i%3 == 0 && i%5 == 0 {
fmt.Print("fizzbuzz ")
} else if i%3 == 0 {
fmt.Print("fizz ")
} else if i%5 == 0 {
fmt.Print("buzz ")
} else {
fmt.Print(i, " ")
}
}
}
Next up, the same logic but expressed more clearly with a switch instead of a series of if...else:
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// Solution 2
package main
import "fmt"
func main() {
for i := 1; i <= 100; i++ {
switch true {
case i%3 == 0 && i%5 == 0:
fmt.Print("fizzbuzz ")
case i%3 == 0:
fmt.Print("fizz ")
case i%5 == 0:
fmt.Print("buzz ")
default:
fmt.Print(i, " ")
}
}
}
Finally, here is a solution that simplifies the conditions but needs a support variable:
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// Solution 3
package main
import "fmt"
func main() {
for i := 1; i <= 100; i++ {
alredayIn := false
if i%3 == 0 {
alredayIn = true
fmt.Print("fizz")
}
if i%5 == 0 {
alredayIn = true
fmt.Print("buzz")
}
if !alredayIn {
fmt.Print(i)
}
fmt.Print(" ")
}
}
Point is, there are countless ways of solving the same problem. Do your best to find the best solution for you.
Power of a number
Let create a program that calculates the nth power of another number, using only consecutive multiplications. For now
we will not worry too much about memory limits. We’ll just try small numbers to avoid the computer from exploding.
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package main
import "fmt"
func main() {
var base, exp, total int = 2, 9, 1
for i := 0; i < exp; i++ {
total *= base
}
fmt.Printf("The result of %d to the power of %d is: %d", base, exp, total)
}
Prime number
Write a program that calculates if a number is prime.
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package main
import "fmt"
func main() {
var num int = 655360001
var isPrime bool = true
for i := 2; i <= num/2; i++ {
if num%i == 0 {
isPrime = false
break
}
}
if isPrime {
fmt.Printf("The number %d is prime.", num)
} else {
fmt.Printf("The number %d is NOT prime.", num)
}
}
This solution has several optimizations that could be made. But for learning purposes we can leave it at that.
To do on your own
These is a small list of problems you can use to practice your coding skills, they are arranged in approximately ascending order depending on difficulty (from easiest to hardest). Good luck!
Note: Attempt to solve the problems on your own, do not just use the reference solutions. For your own sake do not cheat when trying to solve the exercises.
Note 2: Remember that the shown answers are just a reference and are not the absolute or best answer for every problem. You can solve each problem in several ways, don’t feel like you have to match my code.
1 Hello world
Create a program that prints to the screen the message "Hello from Go land!".
package main
import "fmt"
func main() {
fmt.Println("Hello from Go land!")
}
2 Hello name
Create a program that defines a variable name, store the name of your best friend in there and print to the screen
the message "Hello {name}! I'm coding in Go" (replace {name} with the content of your variable called name)
package main
import "fmt"
func main() {
name := "Alice"
fmt.Printf("Hello %s", name)
}
3 Hello bob
Modify the previous program so that only if the name is "bob" the greeting will be printed in the screen.
package main
import "fmt"
func main() {
name := "alice"
if name == "bob" {
fmt.Printf("Hello %s", name)
}
}
4 Max number
Create a program that prints the maximum between 2 numbers.
package main
import "fmt"
func main() {
var num1, num2, max = 15, 35, 0
if num1 > num2 {
max = num1
} else {
max = num2
}
fmt.Printf("The max between %d and %d is: %d", num1, num2, max)
}
5 Sum of numbers
Make a program that calculates the sum of all the numbers from 1 to 100 (i.e.: 1 + 2 + 3 + 4 + ... + 100) and prints
the result to the screen.
package main
import "fmt"
func main() {
var from, to, sum int = 1, 100, 0
for i := from; i <= to; i++ {
sum += i
}
fmt.Printf("The sum from %d to %d is: %d", from, to, sum)
}
6 Star rating
Make a program that prints stars(*) depending on a variable numStars (e.g.: if numStars is 3 print ***). Note: the
range of stars goes from 0 to 5.
Answer 1:
package main
import "fmt"
func main() {
numStars := 3
for i := numStars; i > 0; i-- {
fmt.Print("*")
}
}
Answer 2:
package main
import (
"fmt"
"strings"
)
func main() {
numStars := 5
fmt.Println(strings.Repeat("*", numStars))
}
7 Sum of multiples
Write a program that calculate the sum of all the multiples of 5 which are less than or equal to a 100. Then print the result to the screen.
package main
import "fmt"
func main() {
var check, target, total = 5, 100, 0
for i := 1; i <= target; i++ {
if i % check == 0 {
total += i
}
}
fmt.Printf("The sum of all mutiples of %d up to %d is: %d", check, target, total)
}
8 Primes up to n
Write a program that prints the prime numbers up to 1000.
package main
import "fmt"
func main() {
for num := 2; num <= 1000; num++ {
isPrime := true
for i := 2; i <= num/2; i++ {
if num%i == 0 {
isPrime = false
break
}
}
if isPrime {
fmt.Printf("%d ", num)
}
}
}
9 Factors of a number
Write a program that prints the prime factors (prime numbers that divide exactly) a given integer (e.g.: the factors of 60 are 2, 3, and 5).
package main
import "fmt"
func main() {
num2Check := 30030
for possibleFactor := 2; possibleFactor <= num2Check/2; possibleFactor++ {
isPrime := true
for i := 2; i <= possibleFactor/2; i++ {
if possibleFactor%i == 0 {
isPrime = false
break
}
}
// We check divisibility only if the number is prime
if isPrime && num2Check%possibleFactor == 0 {
fmt.Printf("%d ", possibleFactor)
}
}
}
Bonus
- Take a close look at the previous exercise Power of a number. Think what will happen to the showed algorithm when the base is negative? Another problem arises when the exp is negative. Describe these problems and propose a solution.
