Scala Programming: Create a new string where 'if' is added to the front of a given string and if the string begins with "if" return the original

Last update on February 05 2025 12:54:25 (UTC/GMT +8 hours)

Write a Scala program to create a new string where 'if' is added to the front of a given string. If the string already begins with 'if', return the string unchanged.

Pre-Knowledge (Before You Start!)

Before attempting this exercise, you should be familiar with the following concepts:

Scala Objects: Understanding how to define objects using the object keyword.
Functions in Scala: How to create functions with parameters and return values.
String Operations: Using methods like startsWith() to check if a string begins with a specific substring.
Conditional Expressions: Using if-else statements for decision-making.
String Concatenation: Understanding how to prepend or append text to a string using +.
Main Method: Understanding the structure of the main() function in Scala.
Printing to Console: Using println() to display results.

Hints (Try Before Looking at the Solution!)

Try to solve the problem using these hints:

Hint 1: Define an object in Scala to contain the function.
Hint 2: Create a function that accepts a string parameter.
Hint 3: Use the startsWith() method to check if the string already begins with "if".
Hint 4: If the string starts with "if", return it unchanged.
Hint 5: If the string does not start with "if", prepend "if " to it.
Hint 6: Use string concatenation to add "if " to the front of the given string.
Hint 7: Call the function in the main() method with different test cases and print the results.

Sample Solution:

Scala Code:

// Define an object named scala_basic
object scala_basic {
  // Define a function named test with a parameter str of type String, returning a String
  def test(str: String): String = 
    {
      // Check if the given string starts with "if"; if true, return the string as is, otherwise, prepend "if "
      if (str.startsWith("if")) str else "if " + str
    }
     
   // Define the main method, which is the entry point of the program
   def main(args: Array[String]): Unit = {
      // Print the result of calling test with the argument "if else"
      println("Result: " + test("if else"))
      
      // Print the result of calling test with the argument "else"
      println("Result: " + test("else"))
    }
}

Sample Output:

Result: if else
Result: if else

Explanation:

Here is the break down of the said Scala code:

object scala_basic {: This declares an object named scala_basic.
def test(str: String): String =: This line defines a function named test that takes a parameter str of type String and returns a String. The function checks if the given string starts with "if". If true, it returns the string as is; otherwise, it prepends "if " to the string.
if (str.startsWith("if")) str else "if " + str: This is a conditional expression inside the test function. It checks if the given string str starts with "if". If true, it returns the string as is; if false, it concatenates "if " with the string and returns the result.
def main(args: Array[String]): Unit = {: This line defines the main method, which is the entry point of the program. It takes an array of strings (args) as its parameter and returns Unit (similar to void in other languages).
println("Result: " + test("if else")): This line calls the "test()" function with the argument "if else", concatenates the result with the string "Result: ", and prints the entire string to the console.
println("Result: " + test("else")): Similar to the previous line, this calls the test function with the argument "else" and prints the result.

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