1 c introduction

A Brief History
Created by Dennis Ritchie at AT&T Labs in 1972
Originally created to design and support the Unix
operating system.
There are only 27 keywords in the original version of C.
– for, goto, if, else ……
Easy to build a compiler for C.Easy to build a compiler for C.
– Many people have written C compilers
– C compilers are available for virtually every platform
In 1983 the American National Standards Institute (ANSI)
formed a committee to establish a standard definition.
– Called ANSI Standard C.
– As opposed to K&R C (referring to the general “standards” that
appeared in the first edition of Brian Kernighan and Ritchie’s
influential book: The C Programming Language)

Why use C?
C is intended as a language for programmers
– BASIC was for nonprogrammers to program and solve simple
problems.
– C was created, influenced, and field-tested by working
programmers.
C is powerful and efficient
– You can nearly achieve the efficiency of assembly code.– You can nearly achieve the efficiency of assembly code.
– System calls and pointers allow you do most of the things that
you can do with an assembly language.
C is a structured language
– Code can be written and read much easier.
C is standardized
– Your ANSI C program should work with any ANSI C compiler.

The C Development Cycle
Edit
Program
Source
Code
Compile
Object
Code
Link Object
Code Executable
Library
Files

“Hello World”
Everyone writes this program first
#include <stdio.h>
int main ( )
{
printf ("Hello, World!n");
return 0;
}

Compilation (1)
Compilation translates your source code (in the file
hello.c) into object code (machine dependent
instructions for the particular machine you are on).
– Note the difference with Java:
The javac compiler creates Java byte code from your
Java program.
The byte code is then executed by a Java virtualThe byte code is then executed by a Java virtual
machine, so it’s machine independent.
Linking the object code will generate an executable file.
There are many compilers for C under Unix
– SUN provides the Workshop C Compiler, which you run with
the cc command
– There is also the freeware GNU compiler gcc

Compilation (2)
To compile a program:
Compile the program to object code.
obelix[2] > cc –c hello.c
Link the object code to executable file.
obelix[3] > cc hello.o –o hello
You can do the two steps together by running:You can do the two steps together by running:
obelix[4] > cc hello.c –o hello
To run your program:
obelix[5] > ./hello
Hello World!
If you leave off the
-o, executable goes into
the file a.out

Compilation (3)
Error messages are a little different than you may be
used to but they can be quite descriptive.
Suppose you forgot the semi-colon after the printf
obelix[3] > cc hello.c –o hello
"hello.c", line 5: syntax error before or at: return"hello.c", line 5: syntax error before or at: return
cc: acomp failed for hello.c
Notice that the compiler flags and informs you about
the error at the first inappropriate token.
– In this case, the return statement.
Always try to fix problems starting with the first error
the compiler gives you - the others may disappear too!

Example 1
#include <stdio.h>
int main ()
{
int radius, area;
printf ("Enter radius (i.e. 10) : ");
scanf ( "%d", &radius);
area = 3.14159 * radius * radius;
printf ("nArea = %dnn", area);
return 0;
}

Example 2
#include <stdio.h>
int main ()
{
int i, j;
for (i = 0; i < 10; i++)
{{
printf ("n");
for (j = 0; j < i+1; j++ )
printf ( "A");
}
printf("n");
return 0;
}

Example 3
/* Program to calculate the product of
two numbers */
#include <stdio.h>
int product(int x, int y);
int main ()
{
int a,b,c;
/* Calculate and display the product */
c = product (a, b);
printf ("%d times %d = %d n", a, b, c);
return 0;
}
/* Functions returns the product of its
/* Input the first number */
printf ("Enter a number between 1
and 100: ");
scanf ("%d", &a);
/* Input the second number */
printf ("Enter another number
between 1 and 100: ");
scanf ("%d", &b);
/* Functions returns the product of its
two arguments */
int product (int x, int y)
{
return (x*y);
}

1 c introduction

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