C# 2008 Programmer's Reference

Beware that using the Parse() method may trigger an exception, as demonstrated here:

string str = '5a';
int num = int.Parse(str); //---format exception---

This statement causes a format exception to be raised during runtime because the Parse() method cannot perform the conversion. A safer way would be to use the TryParse() method, which will try to perform the conversion. It returns a false if the conversion fails, or else it returns the converted value in the out parameter:

int num;
string str = '5a';
if (int.TryParse(str, out num)) Console.WriteLine(num);
else Console.WriteLine('Cannot convert');

Flow Control

In C#, there are two ways to determine the selection of statements for execution:

□ if-else statement

□ switch statement

if-else Statement

The most common flow-control statement is the if-else statement. It evaluates a Boolean expression and uses the result to determine the block of code to execute. Here's an example:

int num = 9;
if (num % 2 == 0) Console.WriteLine('{0} is even', num);
else Console.WriteLine('{0} is odd', num);

In this example, if num modulus 2 equals to 0, the statement '9 is even' is printed; otherwise (else), '9 is odd' is printed.

Remember to wrap the Boolean expression in a pair of parentheses when using the if statement.

If you have multiple statements to execute after an if-else expression, enclose them in {}, like this:

int num = 9;
if (num % 2 == 0) {
 Console.WriteLine('{0} is even', num);
 Console.WriteLine('Print something here...');
}
else {
 Console.WriteLine('{0} is odd', num);
 Console.WriteLine('Print something here...');
}

Here's another example of an if-else statement:

int num = 9;
string str = string.Empty;
if (num % 2 == 0) str = 'even';
else str = 'odd';

You can rewrite these statements using the conditional operator (?:), like this:

str = (num % 2 == 0) ? 'even' : 'odd';
Console.WriteLine(str); //---odd---

?: is also known as the ternary operator.

The conditional operator has the following format:

condition ? first_expression : second_expression;

If condition is true, the first expression is evaluated and becomes the result; if false, the second expression is evaluated and becomes the result.

switch Statement

You can evaluate multiple expressions and conditionally execute blocks of code by using if- else statements. Consider the following example:

string symbol = 'YHOO';
if (symbol == 'MSFT') {
 Console.WriteLine(27.96);
} else if (symbol == 'GOOG') {
 Console.WriteLine(437.55);
} else if (symbol == 'YHOO') {
 Console.WriteLine(27.15);
} else Console.WriteLine('Stock symbol not recognized');

One problem with this is that multiple if and else-if conditions make the code unwieldy — and this gets worse when you have lots of conditions to check. A better way would be to use the switch keyword:

switch (symbol) {
case 'MSFT':
 Console.WriteLine(27.96);
 break;
case 'GOOG':
 Console.WriteLine(437.55);
 break;
case 'YHOO':
 Console.WriteLine(27.15);
 break;
default:
 Console.WriteLine('Stock symbol not recognized');
 break;
}

The switch keyword handles multiple selections and uses the case keyword to match the condition. Each case statement must contain a unique value and the statement, or statements, that follow it is the block to execute. Each case statement must end