Chapter 1: Introduction to C#

This Chapter will introduce you to C#. You will learn how to write and compile C# programs, C# syntaxes, data types, control flow, classes and their members, inter-faces, arrays, and exception handling I'll begin with an overview of the language.

Control Flow and Program Logic

Control flow and program logic are of the most important parts of a programming language's dynamic behavior. In this section, I'll cover control flow in C#. Most of the condition and looping statements in C# comes from c and C++. Those who are familiar with java will recognize most of them, as well.

The if . . .else Statement

The if . . .else statement is inherited from C and C++. The if . . .else statement is also known as a conditional statement. For example:

if (condition)
statement
else
statement

The if. . .section of the statement or statement block is executed when the condition is true; if it's false, control goes to the else statement or statement block. You can have a nested if . . .else statement with one of more else blocks.

You can also apply conditional or ( || ) and conditional and (&&) operators to combine more then one condition. Listing 1-23 shows you how to use the if. . .else statement.

Listing 1-23 the if . . . else statement example

using System;
public class MyClass
{
          public static void Main()
          {
                   int num1 = 6;
                   int num2 = 23;
                   int res = num1 + num2;
                   if (res > 25)
                   {
                             res = res - 5;
                             Console.WriteLine("Result is more then 25");
                   }
                   else
                   {
                             res = 25;
                             Console.WriteLine("Result is less then 25");
                  }

                    bool b = true;
                   if (res > 25 || b)
                             Console.WriteLine("Res > 25 or b is true");
           else if ( (res>25) && !b )
                   Console.WriteLine("Res > 25 and b is false");
                   else
                    Console.WriteLine("else condition");
          }
}

The switch Statement

Like the if . . . statement, the switch statement is also a conditional statement. It executes the case part if it matches with the switch value. If the switch value doesn't match the case value, the default option executes .The switch statement is similar to an if . . . statement with multiple. . .else conditions, but it tends to be more readable. Note that in C#, you can now switch on string, which is something C++ did not previously allow. See listing 1-24 for an example of a switch statement.

Listing 1-24. The switch statement example

int i = 3;
switch(i)
{
case1:
Console.WriteLine("one");
break;
case2:
Console.WriteLine("two");
break;
case3:
Console.WriteLine("three");
break;
case4:
Console.WriteLine("four");
break;
case5:
Console.WriteLine("five");
break;
default:
Console.WriteLine("None of the about");
break;
}

The for loop Statement

The for loop statement is probably one of the widely used control statements for performing iterations in a loop. It executes a statement in the loop until the given guard condition is true. The for loop statement is a pretest loop, which means it first tests if a condition is true and only executes if it is. You can use the ++ or - operators to provide forward or backward looping. The following is an example of a for loop statement:

// Loop will execute 10 times from 0 to 9
for (int i=0; i<10; i++)
{
Console.WriteLine(i.ToString( ) );
}

The while loop Statement

The while loop statement also falls in the conditional loop category. The while loop statement executes unit the while condition is true. It's also a pretest loop, which means it first tests if a condition is true and only continues execution if it is in the example shown here, the while loop statement executes until the value of i is less then 10;

int i = 0;
while (i<10)
{
Console.WriteLine(i.ToString());
i++;
}

The do . . . while loop Statement

The do . . . while loop statement is a post- test loop, which means it executes a statement first and then checks if the condition is true. If the condition is true, the loop continues until the condition is false. As the name says, "do something while something is true." This is an example of a do . . . while loop:

do
{
Console.WriteLine(i.ToString());
i++;
} while (i<10);

The foreach loop statement

The foreach loop statement is new concept to C++ programmers but will be familiar to veteran visual basic programmers. The foreach loop enables you to iterate over each element of an array or each element of a collection. This is a simple example:

//foreach loop
string[] strArr = {"Mahesh", "Chand", "Test String"};
foreach (string str in strArr)
Console.WriteLine(str);

In this example, the loop will continue until the items in the array are finished. Many of the collection examples in this article will use this loop.

The go to statement

The goto statement is used when you need to jump to a particular code segment. It's similar to the goto statement in visual basic or C++.

In the following code, if an item of array is found, the control goes to the level found and skips all code before that.

Most programmers avoid using the goto statement, but you may find a rare need for it. One such occasion is the use of fall-through on a switch statement. Fall- thought is the ability for the control flow to fall from one case statement directly into another by leaving out the break statement. In C#, fall-though in a switch statement is not allowed as it was in C++. However, if you explicitly tell the switch statement to go to the next label, it will perform a jump to the next case, essentially carrying out the same function as a fall-through. Note that when using a go to in a case statement, you don't have to provide a break (in all other cases, a break statement is mandatory). in this is bill" and "sometimes I'm called William" are displayed on the screen:

Console.WriteLine("What is your name? ");
          string name = Console.ReadLine();
          switch(name)
          {
                   case "Bill":
                             Console.WriteLine("My name is Bill.");
                             goto case "William";
                   case "William":
                   Console.WriteLine("Sometimes I'm called William.");
                             break;
                   case "Anne":
                             Console.WriteLine("My name is Anne. ");
                             break;
                   default:
                             break;
}

The break statement

The break statement exits from a loop or a switch immediately. The break statement is usually applicable when you need to release control of the loop after a certain condition is met, or if you want to exit from the loop without executing the rest of the loop structure. You use it in for, foreach, while, and do. . . while loop statements. The following code shows the break statement. If condition j == 0 is true control will exit from the loop:

for (int i=0; i<10; i++)
{
int j = i*i;
Console.WriteLine(i.ToString());
if (j == 9)
break;
Console.WriteLine(j.ToString());
}

The continue Statement

Similar to the break statement, the continue statement also works in for, foreach, while, and do . . . while statements. The continue statement causes the loop to exit from the current iteration and continue with the rest of the iterations in the loop. See the following code for an example:

for (int i=0; i<10; i++)
{
int j = i*i;
Console.WriteLine("i is "+ i.ToString());
if (j == 9)
Continue;
Console.WriteLine("j is "+ j.ToString());
}

In this code snippet, when the condition j == 9 is true, the control exits from the current iteration and moves to the next iteration.

Note: The break statement makes control exits the entire loop, but the continue statement only skips the current iteration.

The return Statement

The return statement returns from a method before the end of that method is reached. The return statement can either a value or not, depending on the method that calls it.

This is an example of a return statement that return nothing, and another where the return statement returns an integer value:

public static void Main()
{
int output = 9 + 6;
if ( output >= 12)
return;
Console.WriteLine ("Output less then 12");
}
public int Sum(int a, int b)
{
return a + b;
}