CS156: Introduction to C

1. CS156: Introduction to C Lecture 1

2. 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. CS156: Introduction to C

3. 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. CS156: Introduction to C

4. 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. CS156: Introduction to C

5. What is Compilation? • Compilation is a process of translating a program into machine readable code. CS156: Introduction to C

6. An Example C Program • All C programs must have a main function. • The program execution begins with the first statement in this function. #include <stdio.h> int main(int argc, char *argv[]) { // Print Hello World printf("Hello, world!\n"); return 0; } Preprocessor Directive Function Comment Function Call Function return value CS156: Introduction to C

7. An Example C Program • #include <stdio.h> • 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 #include <stdio.h> int main(int argc, char *argv[]) { // Print Hello World printf("Hello, world!\n"); return 0; } Preprocessor Directive Function Comment Function Call Function return value CS156: Introduction to C

8. An Example C Program • 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 #include <stdio.h> int main(int argc, char *argv[]) { // Print Hello World printf("Hello, world!\n"); return 0; } Preprocessor Directive Function Comment Function Call Function return value CS156: Introduction to C

9. The type of main • main() returns an int • main() does not return void I don’t 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. CS156: Introduction to C

10. An Example C Program • // Print Hello World • Comment • Begins with // • The rest of the line is ignored by the compiler #include <stdio.h> int main(int argc, char *argv[]) { // Print Hello World printf("Hello, world!\n"); return 0; } Preprocessor Directive Function Comment Function Call Function return value CS156: Introduction to C

11. An Example C Program • printf ( “Hello, world!\n” ); • printf = name of method • In ( ) are parameters • printf prints the parameter values to the screen • \n = new line character #include <stdio.h> int main(int argc, char *argv[]) { // Print Hello World printf("Hello, world!\n"); return 0; } Preprocessor Directive Function Comment Function Call Function return value CS156: Introduction to C

12. An Example C Program • return 0; • The method main has a return type of int,so we must return an integer value #include <stdio.h> int main(int argc, char *argv[]) { // Print Hello World printf("Hello, world!\n"); return 0; } Preprocessor Directive Function Comment Function Call Function return value CS156: Introduction to C

13. 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. CS156: Introduction to C

14. 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. CS156: Introduction to C

15. Common gcc Options • Many gcc options you won’t need to remember, but some are used often. • -o file – place output in a file named fileinstead 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 CS156: Introduction to C

16. Example Continued preisner> ls hello_world.c preisner> cat hello_world.c #include <stdio.h> 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 12:15 a.out -rw------- 1 cs156 class 95 Feb 20 12:10 hello_world.c preisner> ./a.out Hello, world! preisner> CS156: Introduction to C

17. Example Continued, using -o preisner> ls hello_world.c preisner> cat hello_world.c #include <stdio.h> 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 12:15 hello -rw------- 1 cs156 class 95 Feb 20 12:10 hello_world.c preisner> ./hello Hello, world! preisner> CS156: Introduction to C

18. Example Continued, using -o preisner> ls hello.c preisner> cat hello.c #include <stdio.h> int main() { // Print Hello World printf("Hello, world!\n"); return 0; } preisner> gcc hello.c preisner>./a.out Hello, world! preisner> CS156: Introduction to C