[C#] C# Control Structure - Selection

📋 This is my note-taking from what I learned in the class “Programming 1 - COMP 100-002”

The Control Structures

Control Structures: Conditional/Selection/Branching

• This structure facilitate selective execution of code.
• In some situation, the code block can be ignored or can be processed.
• In C#, this is done with the “if” and the “switch” statements.
• The latter is easier to understand but limited to test equality for ints, chars, and strings.
• This allow you to write any program that is can be programmed (i.e. computable)
• Also called branching or selection because control is divided.

if Statement

1. Uses assertions and code blocks.

2. Assertion is a Boolean expression.

   • You may use the relational operators (==, !=, <, <=, >, >=) to build a Boolean expression.

3. A code block can be a single statement OR a set of statements enclosed within a pair of curly braces.

   • In an if-statement, there are normally 2 blocks - true and false block.

Syntax

if (<<bool expression>>)
{
  <<true block>>
}
else
{
  <<false block>>
}

if (weight > 100)
{
  Console.WriteLine("Heavy");
}
else
{
  Console.WriteLine("Not heavy");
}

using System;
public class Program
{
  public static void Main()
  {
    Console.Write("Enter your age: ");
    int age = Convert.ToInt32(Console.ReadLine());

    if (age < 0)
    {
      Console.WriteLine("Age cannot be negative");
    }
  }
}

Console.Write("Enter an integer: ");
int number = Convert.ToInt32(Console.ReadLine());

if (number % 2 == 0)
{
  Console.WriteLine($"{number} is even");
}
else //you don’t need to check for odd. Why?
{
  Console.WriteLine($"{number} is odd");
}

Console.Write("Are you married (True/False)?: ");
bool isMarried = Convert.ToBoolean(Console.ReadLine());

if (isMarried) //the value in the assertion is already bool
{
  Console.WriteLine("Sorry this is a singles only club.");
}
else
{
  Console.WriteLine("Welcome.");
}

Tips

1. Always use a pair of braces to enclosed your true code block or your false code block.

2. Use positive logic.

   • if(a == b) // positive logic
   • if(!a == b) // negative logic

3. The selection statement is best described using a Flowchart.

Note this!

• The Selection Control Structures adds immense power to the language.
• Selection statements can be nested to do almost everything.
• Another selection statement is the switch-statement.

---

Back to Top

See other articles in Category CS