C is a simple programming language with a relatively simple to understand syntax and few keywords.
C is useless.C itself has no input/output commands, doesn't have support for strings as a fundamental data type. There is no useful math functions built in.
C requires the use of libraries as C is useless by itself. This increases the complexity of the C.The use of ANSI libraries and other methods,the issue of standard libraries is resolved.
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C Programming :: A Quick Hellow World Program
Let's give a simple program that prints out "Hello World" to standard out. We'll call our program as hello.c.
#include
main() {
printf("Hello, world!\n");
return 0;
}
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Explanation of The Above Code:
#include
What is header file?They contain prototypes and other compiler/pre-processor directive.Prototypes are also called the basic abstract function definitions.
Some common header files are stdio.h,stdlib.h, unistd.h and math.h.
main()- This is a function, in particular it is the main block.
{ } - These curly braces are equivalent to the stating that "block begin" and "block end".These can be used at many places,such as switch and if statement.
printf() - This is the actual print statement which is used in our c program fraquently.we have header file stdio.h! But what it does? How it is defined?
return 0-What is this? Who knows what is this
Seems like trying to figure out all this is just way too confusing.
Then the return 0 statement. Seems like we are trying to give something back, and it gives the result as an integer. Maybe if we modified our main function definition: int main() ,now we are saying that our main function will be returning an integer!So,you should always explicitly declare the return type on the function.
Let us add #include
printf always returns an int. The main pages say that printf returns the number of characters printed.It is good programming practice to check for return values. It will not only make your program more readable, but at the end it will make your programs less error prone. But we don't really need it in this particular case.So we cast the function's return to (void). fprintf,exit and fflush are the only functions where you should do this.
What about the documentation? We should probably document some of our code so that other people can understand what we are doing. Comments in the C89 standard are noted by this: /* */. The comment always begins with /* and ends with */.
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An Improved Code of The Above Example
#include
/* Main Function
* Purpose: Controls our program, prints Hello, World!
* Input: None
* Output: Returns Exit Status
*/
int main() {
(void)printf("Hello, world!\n");
return EXIT_SUCCESS;
}
Note:
The KEY POINT of this whole introduction is to show you the fundamental difference between understandability and correctness. If you lose understandability in an attempt to gain correctness, you will lose at the end. Always place the understandability as a priority ABOVE correctness. If a program is more understandable in the end,the chances it can be fixed correctly will be much higher. It is recommend that you should always document your program. You stand less of a chance of screwing up your program later,if you try to make your program itself more understandable.
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The advantages of C
In other words,for writing anything from small programs for personal amusement to complex industrial applications,C is one of a large number of high-level languages designed for general-purpose programming.
C has many advantages:
Before C,machine-language programmers criticized high-level languages because,with their black box approach,they shielded the user from the working details of all its facilities and the computer. To give access to any level of the computer down to raw machine language,however, C was designed and because of this, it is perhaps the most flexible high-level language.
To organize programs in a clear,easy,logical way,C has features that allow the programmer.For example,C allows meaningful names for variables without any loss of efficiency, yet it gives a complete freedom of programming style,a set of flexible commands for performing tasks repetitively (for, while,do) and including flexible ways of making decisions.
C is also succinct. It permits the creation of tidy and compact programs. This feature can be a mixed blessing, however, and the C programmer must balance readability and simplicity.
C allows commands that are invalid in some other languages. This is no defect, but a powerful freedom which, when used with caution, makes many things easily possible. It does mean that there are concealed difficulties in C, but if you write thoughtfully and carefully, you can create fast, efficient programs.
With C, you can use every resource of your computer offers. C tries to link closely with the local environment, providing facilities for gaining access to common peripherals like printers and disk drives.
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The C Compilation Model
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Creating, Compiling and Running Your Program
Creating the program
First create a file containing the complete program, such as the above example. You can use any ordinary editor to create the file. One such editor is textedit which is available on most UNIX systems.
The filename must have extension ``.c'' (full stop, lower case c), e.g. myprog.c or progtest.c. The contents must have to obey C syntax. For example, they might be as in the above example,starting with the line /* /* end of the program */.
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Compilation
There are many C compilers are present around. The cc is being the default Sun compiler. The GNU C compiler gcc is popular and also available for many platforms. PC users may also be familiar with Borland bcc compiler.
There are also C++ compilers which are usually denoted by CC (note upper case CC.For example Sun provides GNU and CCGCC. The GNU compiler is also denoted by the command g++
Other C/C++ compilers also exist. All the above compilers operate in essentially the share many common command line options and same manner. However, the best source of each compiler is through online manual pages of your system: e.g. man cc.
In the basic discussions of compiler operation,for the sake of compactness,we will simply refer to the cc compiler -- other compilers can simply be substituted in place of cc until and unless otherwise stated.
Your program simply invoke the command cc to Compile . The command must be followed by the name of the (C) program you wish to compile it.
The compilation command is:
cc program.c
where program.c is name of the file.
If there are obvious errors in your program (such as mistypings, misspelling one of the key words or omitting a semi-colon), the compiler will detect it and report them.
It may possible that the compiler cannot detect logical errors.
If the compiler option -o is used : the file listed after the -oor when the compiler has successfully digested your program, the compiled version, or executable, is left in a file called a.out
It is convenient to use a -o and filename in the compilation as in
cc -o program program.c
which puts the compiled program into the file program ( any file you name following the "-o" argument) instead of putting it in the file a.out .
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Running the program
The next stage is to run your executable program.You simply type the name of the file containing it, in this case program (or a.out),to run an executable in UNIX.
This executes your program able to print any results to the screen. At this stage there may be run-time errors, such as it may become evident that the program has produced incorrect output or division by zero.
If so, you must return to edit your program source, and compile it again, and run it again.
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C is a High Level Language
C is also called as a high-level language. To give a list of instructions (a computer program) to a computer,the high-level computer language is used. The native language of the computer is a stream of numbers called machine level language. As you might expect, the action resulting from a single machine language instruction is very primitive, and many thousands of them can be required to do something like substantial. A high-level language provides a set of instructions you can recombine creatively and give to the imaginary black boxe of the computer. The high-level language software will then translate these high-level instructions into the low-level machine language instructions
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Characteristics of C
We briefly list some of C's characteristics that have lead to its popularity as a programming language and define the language. Naturally we will be studying many of these aspects throughout our tutorial.
Extensive use of function calls
Small size
Loose typing -- unlike PASCAL
Structured language
Low level (BitWise) programming readily available
Pointer implementation - extensive use of pointers for memory, array, structures and functions.
C has now become a widely used professional language for various reasons.
It has high-level constructs.
It produces efficient programs.
It can handle low-level activities.
It can be compiled on a variety of computers.
The main drawback of c is that it has poor error detection which can make it off putting to the beginner. However diligence in this matter can pay off handsomely since having learned the rules of the C we can break them. Not all languages allow this. This if done carefully and properly leads to the power of C programming.
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C Program Structure
A C program basically has the following form:
Preprocessor Commands
Function prototypes -- declare function types and variables passed to function.
Type definitions
Variables
Functions
We must have a main() function
C assumes that function returns an integer type,if the type definition is omitted. NOTE: This can be a source of the problems in a program
/* Sample program */
main()
{
printf( ``I Like C \n'' );
exit ( 0 );
}
NOTE:
printf is a standard C function -- called from main.
C requires a semicolon at the end of the every statement.
\n signifies newline. Formatted output -- more later.
exit() is also a standard function that causes the program to terminate. Strictly speaking it is not needed here as it is the last line of main() and the program will terminate anyway.
