01-core-packages.md

Core Packages

Take me to the lab!

Help for the VSCode editor.

1. Given a string str:= "I love football" . Select the correct function call to replace the word I with We.

   • ReplaceAll( "I", "We", str)
   • ReplaceAll( str, "I", "We")
   • ReplaceAll( str, "We", "I")
   • ReplaceAll( str, "We", "I", "I love football")

   Reveal

   ReplaceAll( str, "I", "We")

   • https://pkg.go.dev/strings#ReplaceAll
2. Write a code in main.go file to read the string in a buffer of size 5 at a time and print the output in each iteration.

   A Go file is located at /root/code/string directory.

   Reveal

   package main
   
   import (
       "fmt"
       "strings"
   )
   
   func main() {
       reader := strings.NewReader("Let us catch up over a cup of coffee")
       // your code goes here
       buf := make([]byte, 5)
       for {
           n, err := reader.Read(buf)
           fmt.Println(buf[:n], err)
           if err != nil {
               break
           }
       }
   
   }

   • The code creates a byte slice of length 5, which will be used as a buffer.
   • The code then enters an infinite loop which repeatedly calls the Read method on the reader object, passing the buffer as an argument.
   • The Read method reads from the input string and fills the buffer with up to 5 bytes of data.
   • It returns the number of bytes read, n, and an error, err.
   • The code then prints the bytes read from the buffer and the error.
   • If the error is not nil, the loop breaks.
   • This will continue until the entire input string has been read and the error returned is io.EOF, indicating the end of the input.
3. For the following file structure, choose the correct file path function call for path to temp.text.

   dir1
   --dir2
   ----dir3
   --------temp.txt
   

   1. filepath.Join("dir1", "../dir1/dir2", "dir3", "temp.txt")

   2. filepath.Join("dir1", "dir2", "dir3", "temp.txt")

   3. filepath.Join("dir2", "../dir1/dir2", "dir3", "temp.txt")

   4. filepath.Join("dir2", "../dir1/dir2//", "dir3", "../dir3/temp.txt")

   (More than one options might be correct)

   • A and B
   • C
   • All of these
   • D
   • B, C and D

   Reveal

   All of these

   package main
   
   import (
       "fmt"
       "path/filepath"
   )
   
   func main() {
       fmt.Println(filepath.Join("dir1", "../dir1/dir2", "dir3", "temp.txt"))
       fmt.Println(filepath.Join("dir1", "dir2", "dir3", "temp.txt"))
       fmt.Println(filepath.Join("dir2", "../dir1/dir2", "dir3", "temp.txt"))
       fmt.Println(filepath.Join("dir2", "../dir1/dir2//", "dir3", "../dir3/temp.txt"))
   }

   The output for this would be:

   dir1/dir2/dir3/temp.txt
   dir1/dir2/dir3/temp.txt
   dir1/dir2/dir3/temp.txt
   dir1/dir2/dir3/temp.txt
   

   Join is used to construct paths in a portable way. It takes any number of arguments and constructs a hierarchical path from them.

4. A text file is given called temp.txt. Write a code in main.go file to open and read from the file in such a way, to produce the following output:

   Lorem Ipsum is simply dummy text of the printing a
   nd typesetting industry. Lorem Ipsum has been the
   industry's standard dummy text ever since the 1500
   s, when an unknown printer took a galley of type a
   nd scrambled it to make a type specimen book.
   

   NOTE: - The output text should have 50 characters per line!

   A Text file is located at the /root/code/book directory with the above content all on one line.

   A Go file is located at the /root/code/book directory for you to edit.

   Reveal

   package main
   
   import (
       "fmt"
       "os"
   )
   
   func main() {
   
       // Open the text file
       f, _ := os.Open("temp.txt")
       // make a 50 byte buffer
       b := make([]byte, 50)
       for {
           // Read 50 bytes (size of the buffer determines this)
           n, err := f.Read(b)
           // Convert the buffer to a string and print it,
           // using a slice to cover the number of bytes read
           // Last block will be less than 50 bytes.
           fmt.Println(string(b[0:n]))
           if err != nil {
               // Exit loop because we have reached end of file
               // err will be `io.EOF`
               break
           }
       }
   }

5. In the following program, throw a custom error with the given statement, for the following cases.

   • If divisor is less than zero: "Division is not supported for negative numbers"
   • If divisor is equal to zero: "Cannot divide by zero"

   A Go file is located at the /root/code/division directory for you to edit

   Reveal

   Complete the divideNumber function like this

   func divideNumber(m int, n int) (int, error) {
       // your code goes here
       if n < 0 {
           return 0, errors.New("Division is not supported for negative numbers")
       }
       if n == 0 {
           return 0, errors.New("Cannot divide by zero")
       }
       return m / n, nil
   }

   And add an import for the errors package, or you'll get a compiler error.

6. What would be the output for the following code?

   package main
   
   import (
       "fmt"
       "sort"
   )
   
   func main() {
   
       var strs = []string{"Apple", "Around", "Armor", "An"}
       sort.Strings(strs)
       fmt.Println(strs)
   }

   • [An Apple Armor Around]
   • []
   • [Around Armor Apple An]
   • Syntax Error

   Reveal

   • [An Apple Armor Around]

   • Strings are sorted in ascending dictionary order.

7. What does log.Fatal do?

   • It prints the log and then raises a panic.
   • It exits the program.
   • It prints the log and then safely exits the program
   • It raises a panic.

   Reveal

   It prints the log and then safely exits the program

8. Solve the syntax errors in main_test.go file, so go test gives a PASS.

   A Go file is located at the /root/code/test directory.

   Reveal

   package main
   import "testing" // <- add this
   
   // add the required argument "t *testing.T"
   func TestHelloWorld(t *testing.T) {
   
       actual := HelloWorld() // <- add this
       if actual != "hello world" {
           t.Errorf("expected 'hello world', got '%s'", actual)
       }
   }

   cd /root/code/test
   go test