WCCI Course Materials

Operators and Expressions


Lesson Goals

  • Learn about the different operators and their functions.
  • Become familiar with C# syntax.

Write practice statements for the arithmetic operators

If variable a holds 10 and variable b holds 15, then:

Operator Operation Description Expression Result
+ addition adds two operands a + b 25
- subtraction subtracts second operand from the first a - b -5
* multiplication multiplies the operands a * b 150
/ division divides first operand by second operand b / a 1
% modulus (remainder) returns the remainder after integer division b % a 5

Write practice statements for the increment
and decrement operators

If variable a holds the value 42, then:

Operator Operation Description Expression Equivalent to… a's value afterwards
++ increment adds one to the value its int operand holds a++ a = a + 1 43
‐‐ decrement subtracts one from the value its int operand holds a-- a = a - 1 41

Write practice statements for the equality operators

If variable a holds 10 and variable b holds 15, then:

Operator Operation Description Expression Result
== equal to evaluates to true if the two operands are equal a == 10
a == b		 true
false
!= not equal to evaluates to true if the two operands are not equal a != 10
a != b		 false
true

Write practice statements for the relational operators

If variable a holds 10 and variable b holds 15, then:

Operator Operation Description Expression Result
> greater than evaluates to true of the first operand is greater than the second operand a > b false
>= greater than or equal to evaluates to true of the first operand is greater than or equal to the second operand a >= b
a >= 10		 false
true
< less than evaluates to true of the first operand is less than the second operand a < b true
<= less than or equal to evaluates to true of the first operand is less than or equal to the second operand a <= b
a <= 10		 true
true

Write practice statements for the logical operators

If variable a holds true and variable b holds false, then:

Operator Operation Description Expression Result
&& conditional AND evaluates to true if both operands are true;
otherwise, evaluates to false		 a && b
a && true		 false
true
|| conditional OR evaluates to true if either operand is true;
otherwise, evaluates to false		 a || b
b || false		 true
false

Translating English to C#.

Let's translate English statements into C#. First, we'll do one together.

Start by writing the statements as comments. Here's an example:

// Jessica is 23 years old.
int jessicaAge = 23;

// Sam is 47.
int samAge = 47;

// Jessica is younger than Sam.
Console.WriteLine(jessicaAge < samAge);

Let's break it down…

Defining a variable to hold Jessica's age:

We need to create a variable to hold the age of Jessica. What should its type be?

// Jessica is 23 years old.

Since we think of ages as whole numbers, we will use an int:

int jessicaAge;

Let's break it down...

Assigning a value for Jessica's age

The word "is" means equals. How do we represent assignment?

// Jessica __is__ 23 years old.

If Jessica "is 23", then Jessica's age = 23:

int jessicaAge = 23;

Let's break it down…

Comparing Jessica's and Sam's ages:

To say Jessica is younger than Sam means we are comparing their ages. Which operator would we use to compare them?

// Jessica is younger than Sam.

We use the "less than" relational operator to perform this comparison:

Console.WriteLine(jessicaAge < samAge);

Let's look at the syntax

Single line comments start with //:

// Jessica is 23 years old.
int jessicaAge = 23;

// Sam is 47.
int samAge = 47;

// Jessica is younger than Sam.
Console.WriteLine(jessicaAge < samAge);

Each statement ends with a semicolon. It acts like a period (.) in English at the end of a sentence.

Let's look at the syntax

The statement:

int jessicaAge = 23;

reads as "Jessica's age is 23."

Let's look at the syntax

WriteLine is a method, so it ends with a set of opening and closing parentheses:

// Jessica is younger than Sam.
Console.WriteLine(jessicaAge < samAge);
//               ^open paren         ^close paren

Inside the parentheses, we find the method arguments. For the WriteLine method, this is what we want to print. In this case, that's whether Jessica is younger than Sam:

Console.WriteLine(jessicaAge < samAge);

Your turn! Try translating these word problems into C#.

  • Lisa is cooking muffins. The recipe calls for 7 cups of sugar. She has already put in 2 cups. How many more cups does she need to put in?
  • At a restaurant, Mike and his three friends decided to divide the bill evenly. If each person paid $13 then what was the total bill?
  • How many packages of diapers can you buy with $40 if one package costs 8?
  • Last Friday Trevon had $29. Over the weekend he received some money for cleaning the attic. He now has 41. How much money did he receive?
  • Last week Julia ran 30 miles more than Pranav. Julia ran 47 miles. How many miles did Pranav run?
  • How many boxes of envelopes can you buy with $12 if one box costs 3?
  • After paying $5.12 for a salad, Norachai has 27.10. How much money did he have before buying the salad?

Just keep coding! Just keep coding!

  • 331 students went on a field trip. Six buses were filled and 7 students traveled in cars. How many students were in each bus?
  • Aliyah had $24 to spend on seven pencils. After buying them she had 10. How much did each pencil cost?
  • The sum of three consecutive numbers is 72. Print these numbers consecutively to the console.
  • The sum of three consecutive even numbers is 48. What is the smallest of these numbers?
  • Maria has boxes. She buys seven more. A week later, half of her boxes are destroyed in a fire, leaving her with 22 boxes. With how many did she start?