Basic Structure of a C++ Program

Now that you have seen variable declaration, C++ expressions, and the basic math operators, let’s take a quick look at the basic  structure of a C++ program. All C++ programs must have a main  function. This is where the program begins.A  function is one or  more statements grouped together in a logical manner to accomplish some goal under a common name. The following is a basic C++ program.

                     int main()

                     {

                        return 0;

                     }

                Now, this program will not do much—in fact, it won’t do anything  useful at all. It is, however, a valid C++ program. It has a main  function that returns an integer value. The main function is where all C++ programs start. This is the starting point for your entire  program. All main functions are required by the ANSI (American  National Standards Institute) standards to return an integer. The integer is a 0 if the program executes fine, and a 1 if some problem is encountered. This was originally done because some operating  systems require any program to return a value telling the operating system that everything is OK. You will see a lot of Windows  programmers use a main function that returns a void like the following.

void main()

                This will work in some cases, but it is not technically correct.  This book endeavors to conform to the ANSI standards and use

return 0.

                The next thing to notice about our sample program is the  presence of brackets. These brackets are C++’s way of establishing borders around any block of code. (Incidentally, C, Java, and  JavaScript™ do the same thing. Learning it here will help you learn  other languages as well.). Every time you see an opening bracket,  {there must be a matching} closing bracket. You will see a lot more about this when we discuss loops, decision structures, and functions. For now, suffice it to say that brackets form borders around blocks of code.

                With all that said, let’s look at a program that has a few  statements.

                 int main()

                 {

                int j;

                          j = 5;

                          j++;

                          return 0;

                 }

                This simple program creates a variable named j, sets the value of that variable to 5, then increments that value by one. This is still  not a particularly exciting piece of code, but it does illustrate the basic structure of a C++ program. Three statements are executed, a 0 is returned to indicate that everything is OK, and there are brackets surrounding the main function. If you carefully examine this code, and follow this template in all your programming, then you will do well!