Branching Out with if and switch in C#.NET

Maker Code 3 of 9 in C#.NET Branching Out with if and switch

widowed (surely I covered all the options oh, wait), or 4 for none of your business To differentiate among these values, you could use the following series of if statements:

if (maritalStatus == 0) { // Must be unmarried // do something } else { if (maritalStatus == 1) { // Must be married // do something

And so on You can see that these repetitive if statements grow tiresome quickly Testing for multiple cases is such a common occurrence that C# provides a special construct to decide between a set of mutually exclusive conditions This control, the switch, works as follows:

switch(maritalStatus) { case 0: // do the unmarried stuff break; case 1: // do the married stuff break; case 2: // do the divorced stuff break; case 3: // do the widowed stuff break; case 4: // get out of my face break; default: // Goes here if it fails to pass a case; // this is probably an error condition break; }

The expression at the top of the switch statement is evaluated In this case, the expression is simply the variable maritalStatus The value of that expression is then compared against the value of each of the cases Control passes to the default clause if no match is found The argument to the switch statement can also be a string:

string s = Davis ; switch(s) { case Davis :

// break; case Smith : // break; case Jones : // break; case Hvidsten : // break; default: // Goes break; }

Using the switch statement involves these severe restrictions: The argument to the switch() must be one of the counting types (including char) or a string Floating-point values are excluded The various case values must refer to values of the same type as the switch expression The case values must be constant in the sense that their value must be known at compile time (A statement such as case x isn t legal unless x is a type of constant) Each clause must end in a break statement (or another exit command, such as return) The break statement passes control out of the switch You can omit a break statement if two cases lead to the same actions: A single case clause may have more than one case label, as in this example:

string s = Davis ; switch(s) { case Davis : case Hvidsten : // Do the same thing whether s is Davis or Hvidsten // since they re related break; case Smith : // do Smith stuff break; default: // Goes here if it doesn t pass any cases break; }

This approach enables the program to perform the same operation, whether the input is Davis or Hvidsten The SwitchSyntaxTest example on the Web site illustrates a variety of advice about using switch The final section of this chapter supplies a small addendum to the switch story You can find the code at csharp102info

The if statement enables a program to take different paths through the code being executed depending on the results of a bool expression This statement provides for drastically more interesting programs than programs without decision-making capability Adding the ability to execute a set of instructions repeatedly adds another quantum jump in capability Consider the CalculateInterest program from the section Introducing the if statement, earlier in this chapter Performing this simple interest calculation by using a calculator (or by hand, using a piece of paper) would be much easier than writing and executing a program If you could calculate the amount of principal for each of several succeeding years, that would even more useful A simple macro in a Microsoft Excel spreadsheet is still easier to handle, but at least you re getting closer What you need is a way for the computer to execute the same short sequence of instructions multiple times known as a loop