Book I: The Basics of C# Programming in C#

Printing USS Code 39 in C# Book I: The Basics of C# Programming

Making decisions if you can Deciding what else to do Looping without going in a circle Using the while and do while loops Using the for loop and understanding scope

onsider this simple program:

using System; namespace HelloWorld { public class Program { // This is where the program starts static void Main(string[] args) { // Prompt user to enter a name ConsoleWriteLine( Enter your name, please: ); // Now read the name entered string name = ConsoleReadLine(); // Greet the user with the entered name ConsoleWriteLine( Hello, + name); // Wait for user to acknowledge the results ConsoleWriteLine( Press Enter to terminate ); ConsoleRead(); } } }

Beyond introducing you to a few fundamentals of C# programming, this program is almost worthless It simply spits back out whatever you entered You can imagine more complicated program examples that accept input, perform some type of calculations, generate some type of output (otherwise, why do the calculations ), and then exit at the bottom However, even a program such as this one can be of only limited use One key element of any computer processor is its ability to make decisions When I say make decisions, I mean that the processor sends the flow of execution down one path of instructions if a condition is true or down another path if the condition is not true Any programming language must offer this fundamental capability to control the flow of execution

The three basic types of flow control are the if statement, the loop, and the jump (I describe one of the looping controls, the foreach, in 6 of this minibook)

The basis of all C# decision-making capability is the if statement (and the basis of all my decisions is the maybe):

if (bool-expression) { // Control goes here if the expression is true } // Control passes to this statement whether the expression is true or not

A pair of parentheses immediately following the keyword if contains a conditional expression of type bool (See 2 of this minibook for a discussion of bool expressions) Immediately following the expression is a block of code set off by a pair of braces If the expression is true, the program executes the code within the braces; if the expression is not true, the program skips the code in the braces (If the program executes the code in braces, it ends just after the closing brace and continues from there) The if statement is easier to understand by looking at a concrete example:

// Make sure that a is not negative: // If a is less than 0 if (a < 0) { // then assign 0 to it so that it s no longer negative a = 0; }

This segment of code ensures that the variable a is nonnegative greater than or equal to 0 The if statement says, If a is less than 0, assign 0 to a (In other words, turn a into a positive value) The braces aren t required C# treats if(bool-expression) statement; as though it had been written if(bool-expression) {statement;} The general consensus (and my preference) is to always use braces for better clarity In other words, don t ask just do it

Consider a small program that calculates interest The user enters the principal amount and the interest rate, and the program spits out the resulting value for each year (This program isn t sophisticated) The simplistic calculation appears as follows in C#:

// Calculate the value of the principal plus interest decimal interestPaid; interestPaid = principal * (interest / 100); // Now calculate the total decimal total = principal + interestPaid;