Introduction to C Programming S Y STEMS

Transcription

1 Introduction to C Programming CS 40: INTRODUCTION TO U NIX A ND L I NUX O P E R AT ING S Y STEMS

2 Objectives Introduce C programming, including what it is and what it contains, which includes: Command line variables If statements and decisions While loops For loops

3 What is Programming? The process of taking a problem and developing a program to solve the problem In others, we re telling a computer what to do

4 Life Cycle of Programming Algorithm Source Program Executable Program Program Results Problem Algorithm Development Program Development Program Translation Program Execution Solution Human Human Program Hardware Syntax Errors Semantic Errors

5 About C Written by Dennis Ritchie in 1972 at Bell Laboratories (now a part of AT&T) Published in 1978 by Brian Kernighan and Ritchie in the book, The C Programming Language General-purpose programming language that: Provides low-level access to memory Provides language constructs to map efficiently to machine instructions Requires minimal run-time support

6 Why C? Practical Many companies and research projects are done in C Many programs still exist in C Portable and hardware independent Extends to most system architectures Efficiency and performance Produces code that runs nearly as fast as code written in lower-level languages

7 Where is C used? Operating systems Language compilers Assemblers Text editors Print spoolers Network drivers Modern programs Databases Language interpreters Utilities

8 Features of C Few keywords Compound data types (e.g. structures, unions) Pointers (e.g. memory, arrays) External standard libraries (e.g. input/output, string manipulation)

9 Pitfalls of C No range checking No warnings of whether what you program is what you really intend to do Limited checking while compiling the program No checking during running the program

10 Command Line Arguments in C Individual command line arguments: argc[0], argc[1], All command line arguments are considered strings (i.e. arrays of characters) Command line argument count: int argc

11 If Statement if (expr) { } else (or else if) { } (NOTE: else is optional)

12 Switch Statement switch (testvalue) { case value1: break; } default: break;

13 While Statement while (expr) { }

14 Do-While Statement do { } while (expr) Same form as the until statement in Bourne shell scripting

15 For Statement for (var = initial step; condition; increment step) { }

16 Expressions Relational operators >, ==, <, <=, >=,!= Arithmetic operators +, -, *, /, %, ++, +=, --, -=, *=, /=, %=

17 Variable Declaration Must be before the variable is used Some of the basic types: int char float double Format: type varname = value; e.g. int count = 0;

18 Variable Assignment Format: varname = value; e.g. count = count + 1; (or count += 1; or count++;)

19 Declaring Arrays Format: type varname = {value1, value2,, valuen}; Examples: char vowels[5] = { a, e, i, o, u }; int primes[10] = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29}

20 Input Function Format: scanf( inputformat, &var1, &var2, ); e.g. scanf( %d %f, &hours, &price);

21 Output Function Format: printf( outputformat, var1, var2, ); e.g. printf( The average is %7.2f, average);

22 Input/Output Format Descriptors Descriptor Type Description of Descriptor %c Specifies a single character field %Nd %Nx %No %N.Mf Specifies an integer decimal field of N characters Specifies an integer hexadecimal field of N characters Specifies an integer octal field of N characters Specifies a float decimal field of N characters, with M decimal places

23 Function Definition type function_name (argument_list) { } return value; type can be, for example, int, char*, float, etc.; return value must match the type declared for the function

24 Special Commands Command #include <library> (e.g. #include <string.h>, #include myheader.h ) return value; void continue break /*comment*/ Meaning A source library reference; <> is for a standard library, while is for a created header Return with value Type used when nothing is returned Makes a loop return to the beginning Makes a loop or switch terminate Insert comments into the source

25 Hello World Program #include <stdio.h> int main(int argc, char* argv[]) { /* Print the statement Hello, world! to the terminal */ printf("hello, world!\n"); return 0; }

26 Compiling the Source Code with Unix Command: cc Without linker options: cc source.c Creates a.out if successful With linker options: cc source.c -lcurses Linker needs the curses library

27 Compiling the Source Code with Linux Command: gcc Without linker options: gcc source.c Creates a.out if successful With linker options: gcc source.c -lcurses Linker needs the curses library