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Arithmetic Operators

From the syllabus

AQA: Be familiar with and be able to use ... (3.1.1.3/4.1.1.3)

  • Addition, subtraction, multiplication, real/float division, integer division (including remainders), exponentiation, rounding, truncation

The table summarises the standard set of arithmetic operators:

Operator Description Example
+ Adds two values int n = a + b;
- Subtracts two values int n = a - b;
* Multiplies two values int n = a * b;
/ Divides dividend by divisor int n = a / b;
% Modulus, remainder after integer division int n = a % b;
++ Increment by one int n = a++;
-- Decrement by one int n = a--;

The operators for addition, subtraction, and multiplication should present no problems as these work just the same as in Mathematics. However, division is less straightforward. When you divide an integer by another integer in C#, the result is also an integer, specifically the integer part of the answer, ignoring anything after the decimal point. The result is always truncated (rounded down), not rounded to the nearest integer.

For example:

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int cake = 15;
cake = cake / 4; // cake will be 3

In this case, the variable cake will contain 3, not 3.75. Conversely, if you use a double type:

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double cake = 15;
cake = cake / 4; // cake will be 3.75

Now, cake will correctly hold 3.75 as it can store decimal values.

The modulus operator % performs integer division but returns the remainder. For instance, 9 % 2 yields 1.

Warning

Integer division by 0 will result in a runtime error, so always ensure your divisor is not zero.

For incrementing and decrementing, C# offers convenient operators:

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int age = 45;
age++; // age is now 46
int x = 3;
x--; // x is now 2

The ++ operator increments a variable, while -- decrements it. These operators can be used either as postfix or prefix, yielding different results:

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int a = 4;
int b = 5;
Console.WriteLine(a + (b++));   // Outputs 9
Console.WriteLine(a + b);       // Outputs 10 (b is now 6)
Console.WriteLine(a + (++b));   // Outputs 11 (b is incremented before the addition)
Console.WriteLine(a + b);       // Outputs 11

What will be printed to the screen after each operation? If you’re uncertain, write the code and check!

C# does not have an operator for exponentiation. Instead, we use the Math class:

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double Result = Math.Pow(2, 3); // Result is 8

Both parameters must be double, and the result is also a double.

To round or truncate values, we utilize methods from the Math class. Here’s an illustration:

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float Number = 3.456789f;
Console.WriteLine(Number);                  // Outputs 3.456789
Console.WriteLine(Math.Round(Number, 2));   // Outputs 3.46
Console.WriteLine(Math.Truncate(Number));    // Outputs 3