Flow and conditions

We have been focusing on sequence so far. With sequence, you can picture instructions flowing through the computer as it executes them one at a time.

Control flow is all about controlling that flow of instructions (hence the name - control flow). Each language has several control flow statements that define a certain flow pattern. Each of these patterns is controlled by a condition which evaluates to true of false - which is known as a boolean value.

Control flow…

• still means that instructions run in sequence.
• allow you to selective run code - also known as branching.
• allow to to repeat code - also known as looping.
• use conditions to determine which path is taken.
• statements give you the ability to implement algorithms in your code.

Boolean values…

• use the bool type in C#.
• are used in control flow statements to determine which path to take.
• include only the values true and false.
• can be created using comparisons:
  • a == b is true with a equals b, otherwise it is false.
  • a != b is true with a does not equal b, otherwise it is false.
  • a < b is true with a is less than b, otherwise it is false.
  • a <= b is true with a is less or equal to than b, otherwise it is false.
  • a > b is true with a is larger than b, otherwise it is false.
  • a >= b is true with a is larger or equal to than b, otherwise it is false.
• can be combined using logical operators:
  • and: a && b is true when both a and b are true, otherwise it is false.
  • or: a || b is true when either or both of a or b are true. It is false when both a and b are false.
• not (!a) allows you to check if something is false: true is not false, and false is not true.

Tip

With control flow you will always be thinking about the condition under which some code should run. Learning to craft these conditions using boolean logic will take practice.

Example

using static SplashKitSDK.SplashKit;
using static System.Convert;

// You can create boolean variables to store true/false values.
// There are also keywords for true and false
bool ready = false;

Write("Enter a number: ");
string line = ReadLine();
int value = ToInt32(line);

// You can calculate boolean values using comparisons like this
bool bigValue = value > 100;

Write("Is that a big value for you? [y/n]: ");
line = ReadLine();

// You can join boolean values using logical operators
// It is big for the user if they entered 'y' or 'Y'
bool bigForUser = (line == "y") || (line == "Y");

// You can join any boolean value using the logical operators
bool bigForBoth = bigForUser && bigValue;