Introduction to C Programming. What is a C program?

Transcription

1 Introduction to C Programming Goals of this section Write a simple C program - Steps Write or develop code Compile Link Execute Add comments to C code Introduction to C-Programming 2-1 What is a C program? A text file containing a sequence of commands (ASCII file). The text file can be written using any text editor such as Notepad Directives - includes libraries that provide intrinsic functions (e.g. sine, cosine etc.) so we don t have to code these Functions - commands we build to do specific operations such as sort a series of numbers Is it difficult? Not really but it needs to be exact Introduction to C-Programming : Introduction to C-Programming 1

2 Code Development Write ASCII (test) file(s) with commands needed to do the job Programming Steps Build or Link Object file(s) are linked together to include all functions, libraries etc and an executable file is produced this is the one you can run Compile ASCII file is converted from plain text to computer object file which contains commands that computer can understand. i.e. machine language- (this might only be temporary files) Execute You can run the file, typically from the command line for our work Introduction to C-Programming 2-3 My First C Program This doesn t do anything but it will (1) compile, (2) link, and (3) execute printf( This is C. ); This will (1) compile, (2) link, and (3) execute and print to the computer screen This is C Introduction to C-Programming : Introduction to C-Programming 2

3 What is: This is referred to as a directive stdio.h is a text file that contains a library of functions such as printf The directive tells the compiler to include the specific file (eg stdio.h) so that functions used in your code are defined and the compiler then knows what to do with them Introduction to C-Programming 2-5 What are the braces? Note that each statement has a semi colon at the end e.g. x = 5 * 2; y = x - 8; We could write as: x = 5 * 2; y = x - 8; But this is not nearly as legible thus not recommended Introduction to C-Programming : Introduction to C-Programming 3

4 Code Components Introduction to C-Programming 2-7 Always begin with this! Introduction to C-Programming : Introduction to C-Programming 4

5 Your Compiler What do typical compilers do? - have a text editor so you can write code - have a compiler that converts from English to machine language (unreadable by humans) - build the executable file - allow execution by clicking on a button or by a commend - debugging capability (more on this later) Introduction to C-Programming 2-9 What compiler will you use? Lecture (or at home): Quincy 2002, free on the web: ftp://ftp.alstevens.com/quincy2002/, also see instructions on class website. Lab, a UNIX based C complier, we will show you how to use it in the lab, also see instructions on class website Introduction to C-Programming : Introduction to C-Programming 5

6 Program Legibility and White Space Which one is easier to read? float x,y;int j;x=5+2;y=4-8;printf( I like beer! ); do ++j;printf( I can t read this ); while (j); NOTE: acceptable to use white space between tokens eg #include<stdio.h> is equivalent to but not #in clude<stdio.h> (see pg 59 for more details) float x,y; int j; x = 5 + 2; y = 4-8; j= -5; printf("i like beer!"); do ++j; printf("i can read this"); while(j); Introduction to C-Programming 2-11 #include <stdlib.h> ÞÞÞ. printf ( style ); Coding Style NOTE: Þ - indicates a blank space declarations and statements in the body of main( ) are indented three spaces - visually highlights the beginning and end of the function body blank line following the #includes indent statements 3 spaces good style is essential facilitates reading, writing and maintenance uses white space and comments so code is easy to understand and visually attractive indentation is crucial indicates intended flow Introduction to C-Programming : Introduction to C-Programming 6

7 Adding Comments to Your Code Why do we need comments? You might look at the code again in two weeks and have no idea what your though process was when you put the code together More importantly, someone else might use your code - need to know what you were doing Introduction to C-Programming 2-13 Comment Syntax comments can be put anywhere in the code where white-space can be used a comment begins with /* and ends with */ /* Example of a comment in the code */ #include <stdlib.h> all text between /* and */ is ignored by compiler /********************************* ** Good comments stand out **********************************/ // another way to add comments may be split over several Lines or use //, but one line only spend time to comment - printf( This code includes comments. ); set aside half an hour a day to do so Introduction to C-Programming : Introduction to C-Programming 7

8 Your Tasks Read Sections 2.1 and 2.2 (Tan and D Orazio, 1999) Download notes from class notes web site and print Prepare for assignment 2 Make sure you have a computer account and a printing card Introduction to C-Programming : Introduction to C-Programming 8