Programming
in C in 7 days!
By: Siamak Sarmady
Part–1: Quick Start with C:
programming language is perhaps the most
popular programming language. C was created in 1972 by Dennis Ritchie at the
Bell Labs in USA as a part of UNIX operating system. C was also used to develop
some parts of this operating system. From that time C programming language has
been the de facto programming language when fast programs are needed or the
software needs to interact with the hardware in some way. Most of the operating
systems like Linux, Windows™, and Mac™ are either developed in C language or
use this language for most parts of the operating system and the tools coming with
it.
This course is a quick course on C
Programming language. In our first lesson we will first write our first C
program. We will then learn about printing to screen, variables and functions.
We assume that you are familiar with at least one of the popular operating
systems.
For this course you can use the following
compilers or Programming Environments.
• Gcc and cc in Unix and Linux operating
systems
• Borland C or Turbo C in DOS operating
system or in Command line environment of windows operating system
• “Bloodshed Dev-Cpp” integrated development
environment (IDE) gives you a complete and compact programming environment. It
comes with “MinGW” and “GCC” C Compilers and you should not need anything else
for this course.
We use “Bloodshed Dev-Cpp” for this course
and we suggest you also use it. “Bloodshed Dev-Cpp” is free and it can be
downloaded from the website http://www.bloodshed.net (currently under the URL
http://www.bloodshed.net/dev/devcpp.html).
Your
first C program:
Let's write our first C program.
Example 1-1: example1-1.c
#include
main()
{
printf("Hello World!\n");
system("pause"); //this line is
only needed under windows
}
Details
of Test program
• #include
Tells C compiler to include the file
"stdio.h" in this point of your C program before starting compile
step. This "include file” contains several definitions, declarations etc.
• main()
C program consist of one or more functions.
Functions are building blocks of C programs. main() function is different from
other functions by that it is the start point of execution. Our program
contains only function while complicated programs may contain thousands.
• {
O pening brace marks the start of a block.
Closing brace will mark its end. This one marks main () function start
• printf("Hello world!");
This line of code prints the statement
between quotation marks on your output screen. \n tells program to start a new
line in output screen.
• Each command line in C ends with
";" character. Control statements are exceptions. You will soon be
able to determine when you must use ; to end a line of code.
• system(“pause”);
The output window will close in Windows™,
immediately after program execution has been finished. In this way you will not
be able to see results of the execution (as it happens very fast). We have put this command to pause the window
and wait for a keystroke before closing the window. You can remove this line from our examples if
you do not use Windows operating system. This command actually sends the
“pause” command to windows operating system and windows runs the its “pause”
command at this point. We will learn more about this command in later lessons.
• }
closes main() function.
This program contains only one function while
complicated programs may contain several functions.
Data
Types and Variables:
C uses several data types of data. These
include characters, integer numbers and float numbers. In C language you must
declare a variable before you can use it. By declaring a variable to be an
integer or a character for example will let computer to allocate memory space
for storing and interpreting data properly.
Naming
a variable:
It is better that you use meaningful names
for your variables even if this causes them to become long names. Also take
this in mind that C is case sensitive. A variable named "COUNTER" is
different from a variable named "counter".
Functions and commands are all case sensitive
in C Programming language. You can use letters, digits and underscore _
character to make your variable names. Variable names can be up to 31
characters in ANSI C language. The declaration of variables must take place
just after the opening brace of a block. For example we can declare variables
for main() function as below code:
main()
{
int count;
float sum,area;
.
.
.
}
First character in a variable name must be a
letter or an underscore character. It cannot be a C programming
language-reserved word (i.e. Commands and pre defined function names etc). An
example for using variables comes below:
Example
1-2:example1-2.c
#include
main()
{
int sum;
sum=12;
sum=sum+5;
printf("Sum is %d",sum);
system("pause");
}
General form for declaring a variable is:
Type name;
The line sum=sum+5; means: Increase value of
sum by 5. We can also write this as sum+=5; in C programming language. printf
function will print the following:
Sum is 17
In fact %d is the placeholder for integer
variable value that its name comes after double quotes.
Common
data types are:
int
integer
long
long integer
float
float number
double
long float
char
character
Other placeholders are:
%d decimal integer
%ld decimal long integer
%s string or character array
%f float number
%e double (long float)
printf () function used in this example
contains two sections. First section is a string enclosed in double quotes. It
is called a format string. It determines output format for printf function.
Second section is "variable list" section.
We include placeholders for each variable
listed in variable list to determine its output place in final
output text of printf function.
Control
characters
As you saw in previous examples \n control
character makes a new line in output. Other control characters are:
\n New line
\t tab
\r carriage return
\f form feed
\v vertical tab
Multiple
functions
Look at this example:
Example
1-3:example1-3.c
#include
main()
{
printf("I am going inside test function
now\n");
test();
printf("\nNow I am back from test
function\n");
system("pause");
}
test()
{
int a,b;
a=1;
b=a+100;
printf("a is %d and b is %d",a,b);
}
In this example we have written an additional
function. We have called this function from inside main function. When we call
the function, program continues inside test () function and after it reached
end of it, control returns to the point just after test() function call in
main(). You see declaring a function and calling it, is an easy task. Just pay
attention that we used ";" when we called the function but not when we
were declaring it.
