Conditionals

In C#, conditionals compare inputs and return a boolean value indicating whether it evaluates to true or false.

Conditional statements include the if, else and else if statements. A shorthand for the if/else statement is the conditional or ternary operator.

If Statement

An if statement evaluates a condition that, when true, will run a code block that follows.

In the example below, three variables are declared and assigned values. Then, an if statement checks for a condition; if it evaluates to true, then the variable of boolean type will change:

var input1 = 10;
var input2 = 10;
var output = false;

if (input1 == input2) {
  output = true; // Sets the output from false to true.
}

If the code above returned true, the code block below will print a statement to the console:

if (output == true) {
  Console.WriteLine("I returned true");
}

Note == means equal and != means not equal.

Else Statements

An else statement is combined with the if statement. In the case that the condition following the if statement returns false, the code block following the else statement will run.

In the example below, three variables are assigned values:

var input1 = 10;
var input2 = 10;
var output = false;

// If the input variables are not equal, the output will be set to true.
if (input1 != input2) {
  output = true;
} else {
  output = false;
}

if (output == true) {
  // If the output is true, the following string will be printed.
  Console.WriteLine("I returned true");
} else {
  // Otherwise, the string within this else block will be printed.
  Console.WriteLine("I returned false");
}

Since the output is false, this will output:

I returned false

Else If Statements

An else if statement comes after an if statement and is used if an extra comparison is needed before an else statement.

// Four variables are declared here.
var input1 = 10;
var input2 = 10;
var input3 = 5;
var output = false;

// If input1 is equal to input3 then set the variable of output to true.
if (input1 == input3) {
  output = true;
// If input1 is equal to input2, then set the variable of output to true as well.
} else if (input1 == input2) {
  output = true;
// If the two conditions above are false, the else code block will run.
} else {
  output = false;
}

if (output == true) {
  Console.WriteLine("I returned true");
} else if (output == false) {
  Console.WriteLine("I returned false");
} else {
  Console.WriteLine("Error");
}

Above, the else if condition was true so the output was reassigned a value of true. This would run the code block in the first if block which will output:

I returned true

Conditional Operator

The conditional operator ?: also known as the ternary operator, checks a boolean output and returns one of two results depending on whether the condition is true or false. The ternary operator can be read in pseudocode as follows:

Is this condition true ? Run this if yes : Run this if no;

In the example below, the condition that is checked is if input1 is equal to 10. If that condition is true, it returns the first string. Otherwise, it returns the second string:

string getInput1(int input1) => input1 === 10 ? "I returned true" : "I returned false";

Console.WriteLine(getInput1(10)); // Output: "I returned true"
Console.WriteLine(getInput1(5)); // Output: "I returned false"

Codebyte Example

Run the following codebyte example to understand how conditionals work in C#:

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