COMP26120: Algorithms and Imperative Programming

Transcription

1 COMP26120 Lecture C1 1/25 COMP26120: Algorithms and Imperative Programming Lecture C1: Introduction to C Pete Jinks School of Computer Science, University of Manchester Autumn 2011

2 COMP26120 Lecture C1 2/25 Review Course-unit Contents: Algorithms C programming Course-unit Approach: Active Learning Reading

3 COMP26120 Lecture C1 3/25 Lecture Outline C Resources Comparing Java and C Input/Output

4 COMP26120 Lecture C1 C 5/25 Motivation New Programming Language Paradigm Concepts Useful for certain applications uncluttered view of hardware ( high-level assembly-code ) performance CV

5 COMP26120 Lecture C1 C 6/25 A little history Originally from late 60 s - published /1990 ISO standard (C89, C90) 1999/2000 ISO standard (C99) 201? (C1X)

6 COMP26120 Lecture C1 Resources 8/25 Online Resources Starting points: Syllabus: programmes/courseunits/syllabus.php?code=comp26120 Course-unit: QandA: resources-for-learning-c (tag: comp261-algorithms+c) Point to: Online C course in Moodle Online Standard C book (Plauger & Brodie) etc.

7 COMP26120 Lecture C1 Resources 9/25 More Resources man pages etc. Book list on syllabus: - The C Programming Language (Kernighan & Ritchie) - C: A Reference Manual (Harbison & Steele) - Expert C Programming (van der Linden)

8 COMP26120 Lecture C1 Resources 10/25 Online C course cbt/ frontpage.html Navigation: begin return map index Themes : Java to C Information Representation Control Flow Program Structuring Input & Output Colour-coding: green, yellow, orange, red Dependencies/Routes (arrows) e.g. use for C labs

9 COMP26120 Lecture C1 Comparing Java and C 12/25 Assumptions You have successfully completed 1st-year Java (or equivalent): you know how to design non-trivial programmes you know how to encode your designs using Java You are going to learn C based on this C and Java have a lot of similarities, and a lot of differences Look at programming concepts, saying for each whether C is similar to Java (but...) different from Java (as follows...)

10 COMP26120 Lecture C1 Comparing Java and C 13/25 SalaryAnalysis You should have seen the Java version (or something very similar) last year. Compare the Java and C versions Check center character: = same in both = in both, but different < = only in.java > = only in.c Start making a list of similarities and differences. Please work with your neighbour(s).

11 COMP26120 Lecture C1 Input/Output 15/25 Streams Moodle theme: Input and Output man stdio etc. Built-in: System.in stdin System.out stdout System.err stderr e.g. System.out.print(...) fprintf(stdout,...)

12 Creating your own Streams Moodle: Input and Output Streams, Manipulating Streams import java.util.scanner; import java.io.file; #include <stdio.h> #include <stdlib.h> Scanner sscan = new Scanner(new File(filen)); FILE *stream= fopen(filen, "r"); if (!stream) { fprintf(stderr, "can t open %s\n", filen); exit(-1); }? fclose(stream); COMP26120 Lecture C1 Input/Output 16/25

13 COMP26120 Lecture C1 Input/Output 17/25 Writing characters Moodle: Character Manipulation, Revisited putchar(ch) character fputc(stream, ch) putchar(ch) is fputc(stdout,ch) printf(...) formatted fprintf(stream,...) sprintf(string,...) printf(...) is fprintf(stdout,...)

14 COMP26120 Lecture C1 Input/Output 18/25 printf Moodle: (Reading and) Writing System.out.print (String.format(...)); printf (...); ("%2d earns %5d, which is %5d %s", i, j, k, s) println("...",...) printf("...\n",...) System.out.println("mean is:\t" + msal); System.out.println("rounds to:\t" + msalr); printf("mean is:\t%f\n" "rounds to:\t%d\n", msal, msalr);

15 COMP26120 Lecture C1 Input/Output 19/25 Reading characters Moodle: Reading (and Writing), Revisited while (salariesscanner.hasnextline()) String data = salariesscanner.nextline(); enum {buffer size = 100}; char data[buffer size]; while (fgets(data, buffer size, stream)) int currentsalary = Integer.parseInt(data); int currentsalary = atoi(data);

16 COMP26120 Lecture C1 Input/Output 20/25 scanf ch=getchar() character ch=fgetc(stream) getchar() is fgetc(stdin) scanf(...) formatted fscanf(stream,...) sscanf(string,...) scanf(...) is fscanf(stdin,...)

17 OMP26120 Lecture C1 Input/Output 22/25 Reading a line of input #define USE_BSD #include <string.h> char * nextline (FILE* stream) { char data [buffer_size]; fgets (data, buffer_size, stream);//test result int len= strlen (data); data[len-1]= \0 ; //test was \n char* temp= strdup (data); //test result return temp; }

18 COMP26120 Lecture C1 Input/Output 24/25 Reading fields from an input line char one[buffer_size], two[buffer_size], three[buffer_size]; sscanf(data, "%s %s %s", one, two, three); Result of sscanf = number of things read or EOF

19 COMP26120 Lecture C1 Input/Output 25/25 Lecture Review C Resources Comparing Java and C Input/Output