Let’s look into Hello World example using C Programming Language.
Before we study basic building blocks of the C programming language, let us look a bare minimum C program structure so that we can take it as a reference in upcoming chapters.
C Hello World Example
A C program basically consists of the following parts:
- Preprocessor Commands
- Functions
- Variables
- Statements & Expressions
- Comments
Let us look at a simple code that would print the words “Hello World“:
#include <stdio.h>
int main()
{
/* my first program in C */
printf(“Hello, World! \n”);
return 0;
}
Let us look various parts of the above program:
- The first line of the program #include <stdio.h> is a preprocessor command, which tells a C compiler to include stdio.h file before going to actual compilation.
- The next line int main() is the main function where program execution begins.
- The next line /*…*/ will be ignored by the compiler and it has been put to add additional comments in the program. So such lines are called comments in the program.
- The next line printf(…) is another function available in C which causes the message “Hello, World!” to be displayed on the screen.
- The next line return 0; terminates main()function and returns the value 0.
Compile & Execute C Program
Let’s look at how to save the source code in a file, and how to compile and run it. Following are the simple steps:
- Open a text editor and add the above-mentioned code.
- Save the file as hello.c
- Open a command prompt and go to the directory where you saved the file.
- Type gcc hello.c and press enter to compile your code.
- If there are no errors in your code, the command prompt will take you to the next line and would generate a.out executable file.
- Now, type a.out to execute your program.
- You will be able to see “Hello World” printed on the screen
$ gcc hello.c
$ ./a.out
Hello, World!
Make sure that gcc compiler is in your path and that you are running it in the directory containing source file hello.c.
C Basic Syntax
This will give details about all the basic syntax about C programming language
including tokens, keywords, identifiers, etc.
You have seen a basic structure of C program, so it will be easy to understand other basic building blocks of the C programming language.
Tokens in C
A C program consists of various tokens and a token is either a keyword, an identifier, a constant, a string literal, or a symbol. For example, the following C statement consists of five tokens:
printf(“Hello, World! \n”);
The individual tokens are:
printf
(
“Hello, World! \n”;
)
Semicolons ;
In C program, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.
For example, following are two different statements:
printf(“Hello, World! \n”);
return 0;
Comments
Comments are like helping text in your C program and they are ignored by the compiler. They start with /* and terminates with the characters */ as shown below:
/* my first program in C */
You cannot have comments within comments and they do not occur within a string or character literals.
Identifiers
A C identifier is a name used to identify a variable, function, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore _ followed by zero or more letters, underscores, and digits (0 to 9).
C does not allow punctuation characters such as @, $, and % within identifiers. C is a case sensitive programming language. Thus, Manpower and manpower are two different identifiers in C. Here are some examples of acceptable identifiers:
Keywords
The following list shows the reserved words in C. These reserved words may not be used as constant or variable or any other identifier names.
Whitespace in C
A line containing only whitespace, possibly with a comment, is known as a blank line, and a C compiler totally ignores it.
Whitespace is the term used in C to describe blanks, tabs, newline characters and comments. Whitespace separates one part of a statement from another and enables the compiler to identify where one element in a statement, such as int, ends and the next element begins. Therefore, in the following statement:
int age;
There must be at least one whitespace character (usually a space) between int and age for the compiler to be able to distinguish them. On the other hand, in the following statement:
fruit = apples + oranges; // get the total fruit
No whitespace characters are necessary between fruit and =, or between = and apples, although you are free to include some if you wish for readability purpose.