Loops
Loops enable blocks of code to be run a number of times depending on the results of an expression, sometimes called the loop-termination criteria.
while
As the name suggests, a while loop continues to execute while the condition expression remains true.
// while loop
int number = 0;
while (number < 3)
{
Console.WriteLine(number);
number++;
}
do
Similar to a while loop, the do loop executes a code block while an expression remains true. Unlike a while loop, a do loop checks the condition after running the code. This means that a do loop will always run at least once.
// do loop
int number = 0;
do
{
Console.WriteLine(number);
number++;
} while (number < 3);
for
The for loop runs a block of code until an expression is false. It is useful when you know the number of times to iterate through the code, such as when iterating through an array.
The basic syntax is as follows:
for (initializer; condition; iterator)
initializer: the initial condition
condition: a Boolean expression to evaluate
iterator: defines what to do after each iteration
In the example below, we first create a string array and then iterate through the array. A couple of things to note, arrays are zero-based, so your initializer i needs to be set to 0. The maximum value to compare against in the condition will be the length of the array, minus 1. After each iteration we’ll increase i by one. This will enable us to iterate through every value in the array.
// for loop
string[] people = new string[] { "Dave", "Peter", "Frank" };
for (int i = 0; i < people.Length; i++)
{
Console.WriteLine(people[i]);
}
foreach
The foreach statement iterates through a collection of values and executes a block of code each time. It is useful for dealing with arrays and Collections types, such as List<>.
// foreach loop
string[] people = new string[] { "Dave", "Peter", "Frank" };
foreach(var person in people)
{
Console.WriteLine(person);
}
Conditional Blocks
Conditional blocks or selection statements provide a mechanism for choosing between alternate blocks of code.
if-then
The most common of the selection statements is the if-then statement that runs different blocks of code depending on the results of a condition. Conditions can be any expression that returns a Boolean, such as comparing two numbers.
// using a single comparison condition
if(myVariable1 > 0)
{
Console.WriteLine("Bigger than zero");
}
else
{
Con
When the condition evaluates to true, the ‘then’ portion of the statement runs. Unlike VB, in C# you don’t need to explicitly use the Then keyword, anything directly after the condition (usually in the curly braces) is the then statement. I said usually in the curly braces, because if your then block consists of only one line of code, you can omit the braces.
// omit the curly braces {} for single lines of code
if(myVariable1 > 0)
Console.WriteLine("Bigger than zero");
The condition can include more than one comparison using logical operators, such as && (and) or || (or)
// using the && (and) logical operator - both expressions must be true
if(myVariable1 == 0 && myVariable2 == 10)
{
Console.WriteLine("Both are true");
}
// using the || (or) logical operator - either expression may be true
if (myVariable1 == 0 || myVariable2 != 10)
{
Console.WriteLine("One value is true");
}
switch
The switch statement runs one of the number of code blocks based on the value of the switch expression. Each code block begins with a case keyword and a value to compare against the switch expression. If the case and switch expression match, the code in that section runs. Instead of each block of code being delineated by curly braces, a jump statement (usually break) is used to exit the switch.
// compare the value of myVariable1 against 3 different case
// the last is the catch-all or default that runs if neither
// of the previous sections offer a match
switch (myVariable1)
{
case 0:
Console.WriteLine("Equal to zero");
break;
case 1:
Console.WriteLine("Equal to one");
break;
default:
Console.WriteLine("Some other number");
break;
}