Appendix A Developing a C Program on the UNIX system

Transcription

1 Appendix A Developing a C Program on the UNIX system 1. Key in and save the program using vi - see Appendix B - (or some other editor) - ensure that you give the program file a name ending with.c - to indicate that it is a C program file. 2. Compile and link the program using cc <program name> This will produce two files: a) an object file with the same name as your original C program except that the extension will be.o b) an executable file (i.e. a program ready to run) called a.out. e.g. cc test.c compiles test.c producing an object program called test.o then automatically links the object program with relevant library files to produce a runnable program called a.out. 3. Run your program by typing a.out If you would prefer your executable program to be called something else then simply copy a.out to a new name. e.g. cp a.out test copies a.out to produce a runnable program called test. Alternatively, when compiling the program you can specify a particular name for the runnable program by using the -0 option followed by the desired name. e.g. cc -0 test test.c This will compile the program test.c producing - as before - an object file called test.o - and then link the program producing an executable file called test. So, the program can now be run simply by typing test. 265

2 Appendix B - Using vi One of the standard editors on the UNIX system is called vi. It is not particularly friendly, but you will quickly learn to use it - and can usually rely on it being available on most UNIX systems. Starting the vi Editor: vi <program name> Make up your own program name - but finish it with a suitable extension for the language you are using - which for C will be.c. e.g. vi test.c (allows you to key in a C program called test.c) Using vi Unlike a word processor you cannot simply start typing - but must tell the editor that you intend to do so by keying <escape> i. Every time you want to change what you are doing - say go from typing in text, to deleting text or saving the file - you will have to tell the editor that you intend to do so by pressing <escape> followed by the appropriate code. <ESC> I <ESC> x <ESC> dd <ESC> A <ESC> followed by an arrow key <ESC> :w <ESC> :w <program name> <ESC> :wq <ESC> :q! insert text delete a character (under the cursor). delete a line add text at the end of the line move around in the text save the program file save the program file with a new name save the program me and quit quit without saving Note that for the last four commands, when the colon (:) is pressed after the <escape> key, a colon will appear at the bottom ofthe screen ready for the w, wq or q! to be typed. Note that UNIXtreats capital letters andsmallletters as different. The vi editor has a wide range of additional commands which will generally be found in one of the manuals for your system. 266

3 Appendix C - The Binary System Our normal system of counting is denary. When we count past nine, we cannot represent 10 in a single digit so we 'carry' and use an additional digit. You could place column headings above a figure to help with additions, etc. (young children would probably do so). The column headings for the denary system would be: s..100s..los..is - so that, for example, the number 271 would be arranged in columns as: In other words, 271 means 2 lots of 100 plus 7lots of 10 plus 1 unit. We use this number system (also called Base 10 because the column headings grow larger - as they move leftwards - by being multiplied by 10) because we have 10 fingers. A computer, however, obviously does not have 10 fingers; it counts by switching electric currents ON (to represent 1) and OFF (to represent 0). If the computer needs to count further than one, it has to carryjust as we have to do if we want to count past 9. A computer, therefore, uses Base2 (i.e the Binary System) to count. It is possible to place column headings above a binary number - these are multiplied by 2 as they move leftwards: So - for example - the binary number would appear as: meaning 1 lot of lot of lot of 1 =25 denary. Think of all the binary digits as being electric lamps - each one representing a column heading. Ifa particular lamp's value is needed to help make up a number, the light is switched ON - otherwise the light is switched OFF. The digit 0 is used to indicate that the light is off - and 1 to indicate that it is on. 0 1 I I 1 ~ ~g- -g- ~ ~! -g--g ON ON ON ON =

4 Converting Binary numbersto Denary e.g. Convert Binary to Denary. Step 1. Arrange the numbers under binary column headings - so that the number finishes in the rightmost (Is) column. (To make the headings - start on the right with 1 - then keep multiplying by 2 as you move to the left - until there are enough headings to cover the whole number.) Step 2. Add all the headings from those columns which contain Is to get the final answer. So, = 51. (The 8 and 4 columns do not contain Is - so they are ignored. So, 1I 0011 in binary can be written as 51 in denary. Converting Denarynumbersto Binary e.g. convert39 to binary Step 1. Write down the binary column headings finishing on the left with the largest binary column heading which is less than the denary number that you are converting. In this case the largest heading which will go into 39 is Step 2. Subtract the largest heading from the number and write a I in that column (i.e. the 32 column in this case). Keep a note of the remainder Step 3. Repeat Step 2 with the remainder (in this case 7) and keep doing so until the whole number has been used up. So, the final answer is: So, 39 Denary can be written as 1001I 1 Binary. 268

5 Signed Binary Numbers Ifa variable is set up as signed (so that it can hold positive or negative values) the most significant bit (i.e, the largest column heading) is used to denote whether the number is positive or negative. Possibly the most common notation is two's complement. The most significant bit's column heading is made negative (all the other columns remain positive). So for a one-byte location, the headings will be: -128, 64,32, 16,8,4,2, 1. For a two-byte location (e.g. a typical integer) the headings are: ,16384,8192,4096,2048, 1014,512, ,64,32,16,8,4,2,1 As for unsigned numbers, the value of a number is found by adding all the column headings that are switched 0" 'g-~ !! -'g-! -'g-ft ON ON ON

6 AppendixD - The Hexadecimal System The Hexadecimal System (i.e. base 16) is a convenient shorthand for Binary and is used - for example - in machine code programming. The column headings for the hexadecimal system are: s 256s 16s Is (multiplying by 16 as you move left) So - for example hexadecimal would mean: I x x JU. =290 denary Because it is necessary to be able to count up to 15 in a single column without carrying - extra characters are needed to represent 10, II, 12, 13 and 14 as single digits; the letters A, B, C, D, E and F are used for this purpose. The Hexadecimal Digits are therefore: ABC D E F ConvertingBinary to Hexadecimal It is far simpler to convert binary to hexadecimal than to tum it into decimal. e.g. Convert BinaryintoHexadecimal. Step I Startingfrom the right, split the binary number into groups of four digits (quartets): llloolll Step 2 Again starting from the right place column headings above the binary digits - treating each quartetas separate Step 3 Now convert each quartet into a hexadecimal digit I 10 =14 Decimal =E Hexadecimal I 1 =7 Decimal =7 Hexadecimal Step 4 Place the hexadecimal digits together. So the answer is E7 Hexadecimal 270

7 Appendix E Character Codes Letters of the alphabet, punctuation marks, control codes - such as carriage return, and numeric digits ready to be sent immediately for display are represented by a character code. One of the most common is ASCIT(American Standard Code for Information Interchange). If a character held in ASCII is sent to an output device such as printer or VOU, the device will automatically output the appropriate characters shape. If, for example, a numeric digit is not held in a character code such as ASCII, it will have to be converted first before the device will recognise it. So, the command printj("%d", numl} will convert the value in numl from pure binary to a suitable character code (one code for each digit of the number) before sending it to the screen for display. However, the command printj("%c". numl) will simply send the binary pattern stored in numl to the screen - on the assumption that it contains a recognisable code for a single digit (or other character). Note that ASCII is a seven bit code, so the most significant bit of a byte (e.g. a character location) is not used. 271

8 ASCllCodes Character Binary Hex Character Binary Hex <NUL> 00000oo o 40 <SOH> A <STX> ()()()()()10 02 B <ETX> ()()()()()II 03 C <EOT> <ENQ> E <ACK> F <BEL> <BS> H <HT> <VT> OA J A <LF> OB K B <FF> OC L C <CR> M <SO> OE N E <SI> OF F <DLE> P <DCl> Q <DC2> R <DC3> S <DC4> T <NAK> U <SYN> IV <ETB> W <CAN> X <EM> Y <SUB> la Z SA <ESC> IB [ B <FS> lc \ C <OS> ) A <RS> IE E <US> IF SF ~ <SP> ! a " b #/ c $ d % e & f g ( h ) i A j A B k C C m E n E / F F p I q r s t u v w x y A z A B ( B < C I C ) > E E? F <DEL> F 272

9 Index #dejine 38 actual parameters 26 addition 11 address 130 Address arithmetic 133 ampersand 9 and 17 ar 221 argc 259 arguments 26, 226 argv 259 Arithmetic 11, 12 arithmetic shift 243 arithmetic signs 11 array 133,137,139,255 Array of pointers 259 Arrays - Single Dimensional 113, 114 Arrays - Two Dimensional 116, 117 Arrays of Pointers 139 Arrays of Pointers to Functions 255 Arrays of Strings 119 Arrays of Structures 121, 122 ASCn 271 Assignment 10, 106 Assignment Operators 12 atof 250 atoi 250 atol 250 automatic 37 binary stream 184 Binary System 267 Bit-fields 245, 247 Bitwise AND 239 Bitwise NOT 242 Bitwise Operators 239 Bitwise OR 240 Bitwise XOR 241 block 21,43,226 bounds checking 114 braces 3, 16, 19,21,43 break 18,44 buffer 50 buffered input 49 Buffered Keyboard Input 50 byte 124 case 18 cast 145,264 cc 215,265 Central Memory 124 char 6,56 character 6, 10 Character Codes 271 Character Type Functions 248 Circular Linked Lists 158 Command Line Arguments 259 comments 4 Comparing Pointers 135 compilation errors 2 Compile 265 compiler 1 Compiling and Linking Modules 215 Conditional Expressions 230 const 237 continue 44 Conversion of Data Types 261 ctype.h 248 Data Types 56 declaration 213 Decrementing 13 default 18 division II do..while 20, 52 Dynamic Memory Allocation 145, 147 end-of-string character 119 enum 40 EOF 193, 194, 198 Evaluating a Condition 52 executable file 265 exit 45 extern 216 extemallinkage 213 extemal variables 35 fclose 186, 189, 191, 194, 196, 199, 206 feof 189, 199 ferror 206 fgetc 198 field 184 FILE 185, 188, 191, 193, 196, 198 Files 184 Files - Handling Errors 205 Files - Reading Data from Disk one byte at a time using getc 198 Files - Reading Data from Disk using fread 188 Files - Reading Formatted Text from Disk using fscanf 193 Files - Storing Data on Disk using fwrite 185 Files - Writing Data to Disk - one byte at a time - using putc 196 Files - Writing Formatted Text to Disk using fprintf 191 float 6 float.h 58 floating point 6 fopen 185, 188, , 196, 198, 205 for

10 formal parameters 26 Formatting Output 46 fprintf 191, 207 fputc 196 fread 188,206 free 146, 153, 161, 170, 183 fseanf 193,207 fseek 200, 208 Functions 22,24,26,28,30,213 Functions - 32 fwrlte 186, 206 getc 198,208 getehar 49, 50 gets 9,50 Global Variables 35,216 goto 44 header file 222 header files 3, 5, 22 Hexadecimal 270 hierarchical 70, 83 Hierarchical Coding 83, 86, 88 if 52 if.. else 14, 15, 16 Implementing a Complex Program Design using Hierarchical Code 90 Implementing a Complex Program Design using In-line Code 79 Implementing a Design 70 Implementing a Program Design 93 in-line 70 In-line Coding 71, 75, 77 Incrementing 13 initialise 10 initialising 19 Input Format 48 int 6,56 integer 6 isalnum 248 isalpha 248 isdigit 248 islower 248 isprint 249 isspace 249 isupper 248 iteration 61,75,86 Keywords 5 label 44 Layout of a C Program 4 Left Shift 243 library 221 library files 3, 265 limits.h 58 link 265 Linked Lists 149 Local Variables 24,226 logic error 2 Logical Operators logical shift 243 long 56 long int 57 loop 19 machine code 1 macro 224, 226 Macros - using Arguments 226 mauoe 145, 147, ISO, 159, 168, 174 Mixing data types 263 Modular Programming 212 module 212 modulus 11 multiplication 11 Nested Structures 109, 111 newline 8 not 17 object file 265 Object Libraries 221 Operations on Structures 106 or 17 out-of-line 70, 83 parameter 106, 130, 137,257 Parameters 26 Passing Arrays as Parameter 137 Passing Function Addresses as Parameter 257 Passing Pointers as Parameters 130 pointer to a function 257 pointer variable 127, 128, 135 Pointers 126, 133, 139 Pointers and Arrays 133 Pointers to Arrays of Pointers 143 Pointers to Functions 251, 255 Pointers to Pointers 142 Pointers to Structures 131 preprocessor 224 print! 3,7,9,46,57 processor 236 Program Design 59 prototype 22 putc 196, 208 putchar 49 Queues 167 Random Files 200 record 184, 188 Recursion 34 recursive 179 register 236 Register Variables 236 relational expression 52 Relational Operators 14 remainder 11 reserved 5 return 3, 28, 44, 107 Right Shift 243 run-time error 2 scanf 7,9,48,50,57 selection 62,77,88

11 semi-colon 3 sequence 60, 71 short 56 short int 57 signed 56 Signed Binary Numbers 269 signed char 56 signed int 56 signed short int 57 sizeof 146 standard library 5 static 37,218 Static Local Variables 37 stdio.h 3 stdlib.h 45, 145,250 storage location 124 strcmp 42 strcpy 42 stream 184 string 106,113,119 String Functions 42 string.h 42 Strings 9, 10 strlen 42 struct 101, 104 structure 111,121,122,131,233,245 Structure Diagrams 59 Structure Types 104, 105 Structures 101, 102, 109 Subscripting Pointers 135 subtraction 11 switch 18 symbolic constant 38, 40 symbolic constants 58 tab 8 Test Plan 97, roo Testing Software 96 text format 184 text stream 184 tolower 249 toupper 249 Trees 173 typedef 228 unbuffered input 49 union 231,232,233 union type 231 Unions and Structures 233 UlVlX 1,215,265,266 unsigned 56 unsigned char 56 unsigned int 56 unsigned long int 57 unsigned short int 57 Using Pointers 128 Variables 6 vi 265,266 Vocabulary 5 void volatile 237 while 19,52 white space characters 50 word 124