CS156: Introduction to C

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CS156 Introduction to C

• Lecture 1

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What is a Program?

• A program is set of instructions for a computer
• Examples Unix, Shell, Find, cd
• A compiled program is translated into a format
  that the CPU can read directly.
• An interpreted program is not translated into
  machine code but executed by an interpreter.

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What is a Programming Language?

• A programming language is a language for
  describing programs.
• Examples C, Java, Perl, VAX Assembly
• Programming languages are defined by a set of
  rules defining valid programs, syntax, and a set
  of meaning for valid programs, semantics.

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What is C?

• C is an imperative programming language.
• C was originally written for use in UNIX, but is
  now used on many operating systems.
• It was designed for writing system software and
  much of UNIX is written in C.
• C is a relatively low-level language that allows
  the programmer great control over how a program
  executes.

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What is Compilation?

• Compilation is a process of translating a program
  into machine readable code.

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An Example C Program
include int main(int argc, char
argv) // Print Hello World printf("Hello,
world!\n") return 0
Preprocessor Directive
Function
Comment
Function Call
Function return value

• All C programs must have a main function.
• The program execution begins with the first
  statement in this function.

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An Example C Program
include int main(int argc, char
argv) // Print Hello World printf("Hello,
world!\n") return 0
Preprocessor Directive
Function
Comment
Function Call
Function return value

• include
• stdio.h
• Standard input/output
• .h header file
• Header files include
• Declaration of functions, macros, templates and
  other prgrmg elements
• include
• Add a copy of the header file to this file during
  compilation

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An Example C Program
include int main(int argc, char
argv) // Print Hello World printf("Hello,
world!\n") return 0
Preprocessor Directive
Function
Comment
Function Call
Function return value

• int main ( int argc, char argv )
• Function header
• int return type (int integer)
• main name of the function
• In ( ) are parameters
• designate beginning and end of function

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The type of main

• main() returns an int
• main() does not return void
• I dont care if it void works for your compiler.
  ANSI says that main() returns int, and ANSI wins
  all arguments.
• We teach ANSI C in this class, not Microsoft C or
  GNU C or any particular compiler.

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An Example C Program
include int main(int argc, char
argv) // Print Hello World printf("Hello,
world!\n") return 0
Preprocessor Directive
Function
Comment
Function Call
Function return value

• // Print Hello World
• Comment
• Begins with //
• The rest of the line is ignored by the compiler

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An Example C Program
include int main(int argc, char
argv) // Print Hello World printf("Hello,
world!\n") return 0
Preprocessor Directive
Function
Comment
Function Call
Function return value

• printf ( Hello, world!\n )
• printf name of method
• In ( ) are parameters
• printf prints the parameter values to the screen
• \n new line character

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An Example C Program
include int main(int argc, char
argv) // Print Hello World printf("Hello,
world!\n") return 0
Preprocessor Directive
Function
Comment
Function Call
Function return value

• return 0
• The method main has a return type of int,so we
  must return an integer value

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Creating a C Program in Unix

• For this class you will be doing all programming
  on the Linux operating system.
• You will create your programs using an editor
  pico, vim or emacs.
• Advanced editors such as vim and emacs provide
  tools that help with program writing.
• Syntax highlighting is the most common tool and
  is very helpful.

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gcc The GNU C Compiler

• The gcc is a front end for a number of
  compilation tools.
• Preprocessor handle directives
• Compiler Convert code to assembly
• Assembler translate assembly to machine code
• Linker combine machine code files into
  executable file
• The gcc is equipped with many options that change
  its behavior. The options affect such things as
  optimization, output format, etc.

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Common gcc Options

• Many gcc options you wont need to remember, but
  some are used often.
• -o file place output in a file named file
  instead of the default file a.out
• -v give verbose output, show the commands
  being executed
• --help give some basic usage information about
  the compiler

preisner gcc o hello hello_world.c
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Example Continued
preisner ls hello_world.c preisner cat
hello_world.c include int main(int
argc, char argv) // Print Hello
World printf("Hello, world!\n") return 0
preisner gcc hello_world.c preisner ls
-l total 16 -rwx------ 1 cs156 class 4705 Feb 20
1215 a.out -rw------- 1 cs156 class 95 Feb 20
1210 hello_world.c preisner ./a.out Hello,
world! preisner
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Example Continued, using -o
preisner ls hello_world.c preisner cat
hello_world.c include int main(int
argc, char argv) // Print Hello
World printf("Hello, world!\n") return 0
preisner gcc o hello hello_world.c preisner
ls -l total 16 -rwx------ 1 cs156 class 4705 Feb
20 1215 hello -rw------- 1 cs156 class 95 Feb
20 1210 hello_world.c preisner ./hello Hello,
world! preisner
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Example Continued, using -o
preisner ls hello.c preisner cat
hello.c include int main() //
Print Hello World printf("Hello,
world!\n") return 0 preisner gcc
hello.c preisner./a.out Hello, world! preisner