Before you start writing programs, you need to study the structure of programs in the C++ programming language. In other words, the structure of programs is the markup of the work area (code area) in order to clearly define the main blocks of programs and syntax. The structure of programs is slightly different depending on the programming environment. We focus on the Microsoft Visual Studio IDE, and therefore the sample programs will be shown specifically for MVS. If you are using a different IDE, then it will not be difficult for you to port code from MVS to other development environments, and you will understand how to do it over time.

Structure of programs for Microsoft Visual Studio.

Line 1 refers to the entry point for a console application, which means that this program can be run through the Windows command line by specifying the program name, such as struct_program.cpp . Line 1 is a single-line comment because it starts with // characters, more about comments will be discussed in the next article. Line 2 includes the header file "stdafx.h" . This file is similar to a container, since the main preprocessor directives are connected in it (those that the compiler connected when creating the console application), auxiliary directives (connected by the programmer) can also be connected right there.

include is a preprocessor directive, i.e. a message to the preprocessor. Lines starting with the # symbol are processed by the preprocessor before the program is compiled.

Preprocessor directives can also be included in lines, starting after the #include "stdafx.h" entry before the start of the main function. Moreover, this way of connecting libraries is the main one, and using "stdafx.h" is an additional possibility to connect header files, which is available only in MVS. From the 4th to the 6th lines, the main function is declared. Line 4 is the function header, which consists of the return type (in this case, int) of this function, and the name of the function, as well as the parentheses that declare the function's parameters.

int - integer data type

Between the curly brackets is placed the main program code, also called the body of the function. This is the simplest program structure. This structure is written in Microsoft Visual Studio. All of the above is also true for other compilers, except for line 2. There is no "stdafx.h" container anywhere except MVS.

Program structure for C++ Builder.

When you create a console application, the New Project Wizard automatically generates the following code:

//preprocessor directive automatically included by the project creation wizard #include int main() ( return 0; )

We see that the function data type is int . This tells us that the function will return some integer value upon completion, in our case 0. Integer because int is the data type for integers such as 4, 5, 6, 456, 233, etc.

The main thing to remember is that if the return data type of the main function is int or any other except void , then you should write a line like this: return<возвращаемое значение>;

In line 2, the vcl.h library is connected - it is automatically connected by the application creation wizard, so you should not delete it, otherwise the project will not be working.

In general, the wizard automatically creates a program structure that is slightly different from those that we have considered, but the essence remains the same.

For example:

int main(int argc, char* argv) ( return 0; )

Such an example structure is generated by the wizard in MVS2010. This main is slightly different. We’ll look at it in more detail later, but I’ll say that this main has this form, since it was originally designed to support Unicode.

Unicode is a character encoding standard that can represent the characters of almost all written languages. We'll talk more about Unicode later.

There are different versions of main , but there's nothing wrong with that, since main was the main function, so it remains so, so everything said above remains relevant.

An example of the structure of an MVS program with linked libraries.

#include "stdafx.h" #include using namespace std; int main() ( )

The name of the connected libraries is written inside the greater than, less than signs. Header files and the name of the included libraries are synonyms.

The syntax for including header files is:

#include<имя заголовочного файла>

Older header files are included like this (this style of including libraries is inherited from the C programming language):

#include<имя заголовочного файла.h>

The difference is that the name is followed by the .h extension.

The C++ programming language is case sensitive. For example:
return 0; - wrong, there will be a compilation error.
return 0; - right!!!

This article discusses the structures of C++ programs in such environments as MVS and Borland. And as you have already noticed, these structures are almost the same. Therefore, this article is relevant for any IDE. If you have not yet decided on the choice of IDE, read.

Structure of a C program.

Using the C programming language in solving economic problems

Programs and data

Advantages of the C language

1) C is a modern language, its structure encourages the programmer to use methods in his work: top-down design, structured programming, modular structure of programs.

2) C is an efficient language. C programs are compact and fast to execute.

3) C - portable or mobile language.

4) C is a powerful and flexible language.

5) Programs written in C are used to solve problems of various levels. C has a number of powerful assembler constructs.

6) C is a convenient language, it is structured and at the same time does not limit the freedom of programmers too much.

7) C is a compiling type language. Because C is a standardized, device-independent, widely available language, applications written in C can often run with little or no modification on a wide variety of computer systems. The computer, despite its speed and computing power, is a simple device that manipulates binary numbers. Some binary numbers are interpreted by the computer as commands, others as data. To make a computer do something useful, you need to write a program.

Programming – programming activities.

Program is a description of the algorithm for solving a problem given in the computer language.

Command – instructions for the next step.

Example teams: С=А+В, where А, В-operands, +- operation.

Operation is what the computer must do according to each command.

operands -participants of the operation, then over what and with what the operation is performed. A set of elementary operations from the ways of their descriptions form a system of commands of the programming language.

Example #1:

#include

(void main(void) //header of the main function of the program

сout<< “Здравствуй, С!\ n”;

1 line: connection of auxiliary libraries focused on input and output of data of different types to the stream.

2nd line: header of the program's main function. Cout statement to output information<< – помещение в класс данных, \n-переход к новой строке вывода.

Program is a sequence of instructions that implement an algorithm, a set of prescriptions that uniquely determine the content and sequence of operations for solving problems.

The use of S.

1. Programs and data.

2. Scheme of program execution on a computer:

Example #1:

#include< stdio.h>

printf ("I study at BSUIR\ n");

1 line: command include preprocessor, which includes the stdio.h file, which describes the printf library function.

Line 2: definition of a function named main that takes no arguments. The main statement is enclosed in curly braces. The main function calls the printf library function to print, given in character sequence. Slash (\n) - literal newline, transition to newline.

To execute the program on PVEM, you must do the following:

1) Write a program in a programming language.

2) Broadcast it in the standard of this language.

3) Associate it with the necessary programs and functions.

4) Load into RAM.

5) Run and get the result.

A translator is a computer program that translates a program written in a programming language into a form that a computer can understand. The output of the compiler is a file with the extension obj. An executable file or load module is a file that contains a compiled and ready-to-execute program. Borland C++ is a development environment for programs that include both a compiler and some other tools.

Structure of a C program.

Any C program consists of one or more functions and elements. Different functions can be given any names. Functions contain instructions (commands) that prescribe actions at a certain step of execution, and the variable stores the values ​​used in the process of these actions. Such actions can be assigning values ​​to variables, checking some condition. The function named main. The execution of any program begins with the main function.

a) The general structure of a C program without referring to a subroutine:

b) The general structure of a C program with reference to subprojects:

Arguments are one of the mechanisms for interaction between functions. The list of arguments in parentheses follows the function name. Curly braces frame the beginning and end of a program. Instructions that make up the body of programs from operators and operands. In C, every statement and every line of function calls ends with a semicolon. The exception is preprocessor commands and function names that appear at the beginning of a program unit. The goal of most programs is to solve the problem through various transformations of the source data. For this it is necessary.

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I hope you have already installed some IDE on your computer and learned how to compile programs in it. If not, then

All programs written in C have a common structure. Which we will talk about in this lesson. Our first program written in the previous step will help us with this.

Let's fill in a simple map. At the moment, we know that programs exist, but we do not know how they are arranged inside. Therefore, our map will look like this.

Fig.1 Map "Structure of C programs." First level.

Throughout the course, we will return to this map, refine it, supplement it with new elements and blocks.

Now attention. Don't be scared! Below is the source code of three simple programs. Your task is to look at them carefully and try to find some pattern in their code (something that is common in every program).

Listing 1. Program 1. Prints "Hello, World!"

#include

Listing 2. Program 2

int main(void) ( int a, b, c; a = 5; b = 10; c = a+b; return 0; )

Listing 3. Program 3

#include int main(void) ( FILE *fp; fp = fopen("input.txt", "w"); fprintf(fp, "This is Sparta!"); fclose(fp); return 0; )

Take your time to watch the continuation of the lesson and the correct answer to this problem. First, try to answer yourself. After that, click the button "Watch the continuation!"

So, the answer is: In all programs above, there is the following construction:

Listing 4. The main function of any C program is the main function.

int main(void) ( return 0; )

What kind of design is this. This is the declaration of the main function. Every program that is written in C has such a function. Whether it is a big program or a small one, a computer game or a "Hello, World!" program written by you or Bill Gates -- if the program is written in C -- it has a main function. . This is the main function of our program, so to speak. When we run a program, we can think of ourselves as running the program's main function.

Let's stop for a second. We seem to have already figured out something about the structure of programs in the C language. Any C program must contain a main function. Let's display this fact on our knowledge map "Structure of C Programs."

Fig.2 Map "Structure of C programs." main function.

Now the map does not bother us with its gaping emptiness. Let's continue our research.

Let me talk a little about the main function and about functions in general.

The function name is preceded by int, which is an abbreviation for the word integer, which is translated from English as "whole". Such a notation means that when the main function completes its work, it must return an integer to the calling program (in our case, this is the operating system). Usually, for the main function, this is the number zero, which notifies the operating system: "They say, everything is fine. There were no incidents."

Have you ever seen error messages on your computer screen? Usually they write something like "The program crashed ... blah blah blah ... Code -314." Here it is about the same. The difference is that when problems occur, the operating system notifies us about this, and when everything is fine, it does not bother us again.

After the function name, the word void is written in parentheses. In general, function arguments are usually written in brackets, but in our case, when void is written in brackets, this means that the function has no arguments. In other words, the main function does not need any additional input from outside to get started. We'll talk about all this in more detail, but for now, just remember that the word void instead of function arguments means that no arguments are required for this function.

Inside the curly brackets is the description of the main function, i.e. exactly what this function is supposed to do.

Before the closing curly brace, we see the return command. It is this command that is responsible for returning the value from the function. Those. look, if the program reached this point, then everything was fine and no errors occurred, which means you can return the value zero.

You may ask, why exactly zero? And the devil knows! It's just the way they usually do it. You can, in principle, return some other integer, such as 100, or -236. As long as it's an integer. Remember int? Therefore, the whole.

So we figured out the main function. One more moment. What is written in curly braces is usually called the "function body" (or function description), and the first part, the one before the curly braces, is called the function header.

Let's go back to our first "Hello, World" program and see what's what.

Listing 5. "Hello, World" program

#include int main(void) ( printf("Hello, World!\n"); return 0; )

Something we now understand in this program. Only two lines remain unclear, let's go in order.

Listing 6. The include directive

#include

This line is a message to the compiler. These messages, which start with the # character, are called compiler directives. Literally: "connect the file stdio.h". During compilation, the contents of the stdio.h file will be inserted instead of this line. Now let's talk a little about this file. stdio.h (from STanDart Input Output) is a header file that describes various standard functions related to input and output.

A reasonable question arises, "Why do we need to write this line? Why do we even need to insert this file here?" This is necessary so that in our program we can use the standard printf () screen output function.

The point is this. Before we use something in our program, we first need to describe it. Imagine the situation, you were asked to bring a chandelier, but you don’t know what it is. It's not clear what to do.

So is the compiler. When it encounters a function, it looks for its description (i.e., what it should do and what it means) at the beginning of the program (from the very beginning until the moment it is used in the program). So, the printf() function is described in the stdio.h file. That's why we connect it. But when we connect it, the compiler will be able to find the printf () function, otherwise it will give an error.

By the way, it is time to supplement our knowledge map. Before the main function, let's add one more block, the block for connecting header files.

Fig.3 Map "Structure of C programs." Header files connection block.

Let's continue with our program.

Listing 7. printf() function

Printf("Hello, World!\n");

In this line, we call the standard printf() function for displaying to the screen. In this simplest case, we pass it one parameter, a string written in quotes, which must be displayed on the screen, in our case it is Hello, World! \n But wait, what is this \n? There was no \n on the screen when the program started. Why then did we write this here? This sequence is a special character that is a command to go to the next line. It's like pressing the Enter key in MS Word. There are several such special characters, all of them are written using the "\" character - a backslash. These special characters are called control characters. Then I will show them to you. Otherwise, exactly what you wrote in double quotes will appear on the screen.

By the way, note that every C command ends with a ";" (semicolon). It's like a dot at the end of a sentence in Russian. In a normal language, we separate sentences with a dot, and in the C programming language, a semicolon separates commands from each other. Therefore, a semicolon is mandatory. Otherwise, the compiler will swear and give an error.

To call a function, you must write its name and specify the parameters passed to it in parentheses. A function can have one or more parameters. Or there may be no parameters at all, in which case you do not need to write anything in brackets. For example, above we called the printf() function and passed it one parameter, the string to be printed to the screen.

By the way, good advice. Since the main function is always present in every program, and literally in every program we need to display something on the screen, I recommend that you immediately create a file with the following blank so that you do not write the same thing every time.

Listing 8. Standard template for C programs.

#include int main(void) ( return 0; )

Well, that seems to be all. This first lesson can be considered completed. Although no, there is one more thing.

The most important thing in this lesson is, of course, the general structure of the program. But in addition, we learned how to display arbitrary text on the screen. It seems that they did not learn anything at all, but even this is enough to, for example, make a small gift to your mother on March 8th.

The source code of the postcard program is in the archive with the source codes of this lesson. Experiment! You will succeed.