Operators and Type Conversion

Arithmetic operators

int a = 17, b = 5;

Console.WriteLine(a + b);  // addition
Console.WriteLine(a - b);  // subtraction
Console.WriteLine(a * b);  // multiplication
Console.WriteLine(a / b);  // division
Console.WriteLine(a % b);  // remainder (modulo)

22
12
85
3
2

Careful: the result of 17 / 5 is 3, not 3.4! When both sides are int, the division is also an integer division and the fraction is thrown away. The remainder operation (%) is used a lot for jobs such as finding out whether a number is even or odd.

The integer division trap

If you want a decimal result, make at least one side a double:

int a = 17, b = 5;

Console.WriteLine(a / b);          // 3
Console.WriteLine((double)a / b);  // 3.4
Console.WriteLine(a / 5.0);        // 3.4

Writing (double) in parentheses is called a type cast. First a is converted to a double, then the division is performed.

Compound assignment and increment

int counter = 10;
counter += 5;   // counter = counter + 5  -> 15
counter -= 3;   // 12
counter *= 2;   // 24
counter++;      // 25
counter--;      // 24

Comparison and logical operators

Comparison operators (==, !=, <, >, <=, >=) always return a bool. Logical operators combine them: && (and), || (or), ! (not).

double voltage = 3.3;
bool isValid = voltage >= 3.0 && voltage <= 3.6;
Console.WriteLine(isValid);   // True

bool alarm = voltage < 3.0 || voltage > 3.6;
Console.WriteLine(alarm);     // False
Console.WriteLine(!alarm);    // True

From text to number: Parse and TryParse

ReadLine gives you text; you have to convert it before doing arithmetic with it.

Console.Write("Resistance (ohm): ");
string? input = Console.ReadLine();

int resistance = int.Parse(input!);       // if invalid, the program stops with an ERROR
Console.WriteLine(resistance * 2);

If the user types "abc", Parse throws an error. For user input, the safer way is TryParse: it tells you as a bool whether it succeeded and puts the result into its out variable.

Console.Write("Voltage (V): ");
string? input = Console.ReadLine();

if (double.TryParse(input, out double voltage))
{
    Console.WriteLine($"The voltage you entered: {voltage} V");
}
else
{
    Console.WriteLine("Please enter a valid number.");
}

TryParse looks at the current regional settings, so which decimal separator is accepted depends on them: with English (US) settings you type 3.3, while on a machine set to Turkish you type 3,3, and typing the wrong one may be read as a different value.

The Convert class and implicit conversion

Conversion from a smaller type to a larger one happens automatically (implicit): an int can be put into a double. Conversion from a larger type to a smaller one may lose information, so you have to write it explicitly:

int whole = 7;
double decimalValue = whole;      // implicit, no problem

double measurement = 9.99;
int truncated = (int)measurement;     // 9: the fraction is dropped, no rounding
int rounded = Convert.ToInt32(measurement);   // 10: rounds

Console.WriteLine($"{truncated} {rounded}");

9 10

Try it yourself

Write a program that takes two numbers from the user (with TryParse) and prints their sum, difference, product and quotient (as a decimal). If the second number is zero, it should print "Cannot divide by zero" instead of dividing.