Understanding the Most Common Control: the for Loop in C#.NET

Print Code-128 in C#.NET Understanding the Most Common Control: the for Loop

The while loop is the simplest and second most commonly used looping structure in C# However, the while loop is used about as often as metric tools in an American machine shop compared to the for loop The for loop has the following structure:

for(initExpression; condition; incrementExpression) { // body of code }

When the for loop is encountered, the program first executes the initExpression expression It then executes the condition If the condition expression is true, the program executes the body of the loop, which is surrounded by the braces immediately following the for command Upon reaching the closed brace, control passes to incrementExpression and then back to condition, where the loop starts over again

In fact, the definition of a for loop can be converted into the following while loop:

initExpression; while(condition) { // body of code incrementExpression; }

You can better see how the for loop works with the following example:

// here is some C# expression or other a = 1; // now loop for awhile for(int nYear = 1; nYear < nDuration; nYear = nYear + 1) { // body of code } // the program continues here a = 2;

Assume that the program has just executed the a = 1; expression Next, the program declares the variable nYear and initializes it to 1 That done, the program compares nYear to nDuration If nYear is less than nDuration, the body of code within the braces is executed Upon encountering the closed brace, the program jumps back to the top and executes the nYear = nYear + 1 clause before sliding back over to the nYear < nDuration comparison The nYear variable is undefined outside the scope of the for loop, which includes the loop s heading as well as its body

Why do you need the for loop if C# has an equivalent while loop The short answer is that you don t the for loop doesn t bring anything to the table that the while loop can t already do However, the sections of the for loop exist for convenience and to clearly establish the three parts that every loop should have: the setup, exit criteria, and increment Not only is this easier to read, but it s also easier to get right (Remember that the most common mistakes in a while loop are forgetting to increment the counting variable and failing to provide the proper exit criteria)

Beyond any sort of song-and-dance justification that I may make, the most important reason to understand the for loop is that it s the loop that everyone uses and it s the one that you ll see 90 percent of the time when reading other people s code The for loop is designed so that the first expression initializes a counting variable and the last section increments it; however, the C# language does not enforce any such rule You can do anything you want in these two sections however, you would be ill-advised to do anything but initialize and increment the counting variable The increment operator is particularly popular when writing for loops (I describe the increment operator along with other operators in 4) The previous for loop is usually written as follows:

for(int nYear = 1; nYear < nDuration; nYear++) { // body of code }

You almost always see the postincrement operator used in a for loop instead of the preincrement operator, although the effect in this case is the same There s no reason other than habit and the fact that it looks cooler (Next time you want to break the ice, just haul out your C# listing full of postincrement operators to show how cool you really are It almost never works, but it s worth a try) The for loop has one variation that I really can t claim to understand If the logical condition expression is missing, it is assumed to be true Thus, for(;;) is an infinite loop You will see for(;;) used as an infinite loop more often than while(true) I have no idea why that s the case