Structure of programming

Fundamental structure of C programming

A simple structure of C programming is as follows.

#include <stdio.h>

int main(void) {


    return (0);

}

Each line has a meaning explained as follows.

#include <stdio.h>  <- Including a header file related to standard IO

int main(void) { <- Beginning of main function


    return (0);     <- Return result of the function

}  <- End of main function

Fundamental rules

• Write ; at the end of line
• Indent if necessary so that structure can be easily understood
• The purpose to comment out is aiming at help reader understanding the source code.
• When you comment out in a line or lines, comment between /* and */. In a case of comment out in a single line, you can comment after //
• Source code is consisted of functions including main function.
• When you write { to express the beginning of function, you had better write soon after it } to express the end of function. (Some of errors are caused by missing })

Compilation and execution

Write below source code, and save it as "hello.c".

#include <stdio.h>

int main(void) {

    printf("Hello\n");

    return (0);

}

printf(   ) is a function to show characters and numerical values of variables.

In order to execute a source code programmed in C language, it must be comiled and executable file must be created. How to compile is as follows.

If you fail in compilation, message such as below will be shown. If so, you have to check your source code including typo (typing error), which is one of major causes for comiliation error. In the below case, the cause was to forget ; after a function of "printf".

$ gcc hello.c
hello.c: In function `main':
hello.c:7: parse error before `return'

If you read the above error message carefully, it says that "parse error before `return'". It means you had better check especially before "return".

After you correct errors, try compilation again. If it succeeds, executable file will be produced. You can check whether it was produced by typing UNIX command, "ls"

The file "a.out" is an executable file. In order to execute it, type as follows. Then, you'll get a message, "Hello".

When you want to name an executable file as a different name, you can name in the below manner. In the below case, the executable file is named as "hello".

In order to execute it, type as follows.