5: Controlling Program Flow in Visual C#.NET

Encode Code128 in Visual C#.NET 5: Controlling Program Flow

Each value represents the total principal after the number of years elapsed, assuming simple interest compounded annually For example, the value of $1,234 at 125 percent is $3,56194 after 9 years Most of the values show two decimal places for the cents in the amount Because trailing zeros are not displayed in some versions of C#, some values may show only a single or even no digit after the decimal point Thus, $1270 may be displayed as 127 If so, you can fix this by using the special formatting characters described in 9 (C# 20 appears to show trailing zeros by default) The CalculateInterestTable program begins by reading the principal and interest values from the user and checking to make sure that they re valid CalculateInterestTable then reads the number of years over which to iterate and stores this value in the variable nDuration Before entering the while loop, the program declares a variable nYear, which it initializes to 1 This will be the current year that is, this number changes each year as the program loops If the year number contained in nYear is less than the total duration contained in nDuration, the principal for this year is recalculated by calculating the interest based on the previous year The calculated principal is output along with the current-year offset The statement decimalRound() rounds the calculated value to the nearest fraction of a cent The key to the program lies in the last line within the block The statement

3, its value will be 4 after this expression This incrementing moves the calculations along from one year to the next After the year has been incremented, control returns to the top of the loop, where the value nYear is compared to the requested duration In the example run, if the current year is less than 10, the calculation continues After being incremented 10 times, the value of nYear becomes 11, which is greater than 10, and program control passes to the first statement after the while loop That is to say, the program stops looping Most looping commands follow this same basic principle of incrementing a counter until it exceeds a previously defined value The counting variable nYear in CalculateInterestTable must be declared and initialized before the while loop in which it is used In addition, the nYear variable must be incremented, usually as the last statement within the loop As this example demonstrates, you have to look ahead to see what variables you will need This pattern is easier after you ve written a few thousand while loops, like I have

When writing while loops, don t forget to increment the counting variable, as I have in this example:

int nYear = 1; while (nYear < 10) { // whatever }

(I left off the nYear = nYear + 1;) Without the increment, nYear is always 1, and the program loops forever This is called an infinite loop The only way to exit an infinite loop is to terminate the program (or reboot) (I guess nothing is truly infinite, with the possible exception of a particle passing through the event window of a black hole) Make sure that the terminating condition can be satisfied Usually, this means your counting variable is being incremented properly Otherwise, you re looking at an infinite loop, an angry user, bad press, and 50 years of poor harvest Infinite loops are a common mistake, so don t get embarrassed when you get caught in one

A variation of the while loop is the dowhile loop In this case, shown as follows, the condition is not checked until the end of the loop:

int nYear = 1; do { // some calculation nYear = nYear + 1; } while (nYear < nDuration);

In contrast to the while loop, the dowhile loop is executed at least once, regardless of the value of nDuration The dowhile loop is fairly uncommon in practice