MT258Computer Programming andProblem Solving Unit 5
UNIT FiveAbstract data and hidden code
Abstract data type (ADT) • A data type is defined by its behavior more so than its representation. • An abstract data type (ADT) is a set of data items and its operations.
Records for typedef • Example : • typedef • struct • { • int month; • int day; • int year; • } • date_t; • date_t datestart; • date_t dateend;
Records for typedef • Example : • typedef struct Rational_type { • int numerator, denominator;} RATIONAL; • RATIONAL temp;
Abstract data type (ADT) #include <stdio.h> typedef struct Rational_type { int numerator, denominator;} RATIONAL; RATIONAL get_rat(void) { RATIONAL temp; printf("Please enter the numerator of a rational number: "); scanf("%d", &temp.numerator); printf("Please enter the denominator of a rational number: "); scanf("%d", &temp.denominator); return temp; } RATIONAL Add_rational (RATIONAL r1, RATIONAL r2) { RATIONAL temp; temp.numerator = r1.numerator * r2.denominator + r2.numerator * r1.denominator; temp.denominator = r1.denominator * r2.denominator; return temp; }
Abstract data type (ADT) void print_rat(RATIONAL rat) { printf("%d / %d",rat.numerator,rat.denominator); } void main() { RATIONAL rat1, rat2, rat_result; rat1=get_rat(); rat2=get_rat(); rat_result = Add_rational(rat1, rat2); printf("The sum of "); print_rat(rat1); printf(" and "); print_rat(rat2); printf(" is "); print_rat(rat_result); printf("\n\n"); printf("Press Enter to bye\n"); fflush(stdin); getchar(); }
Abstract data type (ADT)
String • A string in C is a group of characters enclosed by double quotes. • Character arrays • String “first” is really a static array of characters • Character arrays can be initialized using string literals char string1[] = "first"; • Null character '\0' terminates strings • string1 actually has 6 elements • It is equivalent to charstring1[]={'f','i','r','s','t','\0'}; • Can access individual characters string1[3] is character ‘s’ • Array name is address of array, so & not needed for scanf scanf("%s",string2); • Reads characters until whitespace encountered • Can write beyond end of array, be careful
Strings • char x[]; • e.g. char x[100]; • Use [ ] to access individual character • indexing begins with 0 • The null character or \0 has the ASCII value zero, which signals the end of a string. • String1[0]=‘\0’; String 1 will be treated as an empty string.
Strings • Example : #include <stdio.h> int main(int argc, char **argv) { char x[10]="computer"; printf ("%c,%c\n",x[1],x[2]); getchar(); return 0; } • Output : o,m
Strings • Example : #include <stdio.h> void main() { char string1[25]=”Hello. I am a C program.”; printf(“first time: %s\n\n”,string1); string1[5] = ‘\0’; printf(“second time: %s\n\n”,string1); printf(“You may press Enter to bye\n”); fflush(stdin); getchar(); } • Output first time: Hello. I am a C program. second time: Hello You may press Enter to bye
Strings • Example : #include <stdio.h> void main() { char string[9]=”Hi there”; printf(“as is | %s|\n”,string); printf(“format 1| %2s|\n”,string); printf(“format 2| %20s|\n”,string); printf(“format 3| %-20s|\n”,string); printf(“You may press Enter to bye\n”); fflush(stdin); getchar(); } • Output as is | Hi there| format 1| Hi there| format 2| Hi there| format 3| Hi there | You may press Enter to bye
Strings • The following are all equivalent. • char hello[] = “Hi there”; • char hello[] = {‘H’,’i’, ‘ ‘,’t’,’h’,’e’,’r’,’e’,’\0’}; • char *hello=“Hi there”; • const char *hello=“Hi there”; • When the keyword const is used, the content cannot be modified.
Two-dimensional array of characters • Example char catNames[5][10]= {“ severe”, “very high”, ” high”,” medium”, ”low”};
Strings • Functions • puts • syntax #include <stdio.h> • int puts(const char *s); • char string[6]=“celia”; • puts(string); • The function puts only accepts a string as its parameter and displays all characters in the string until \0 is encountered.
Strings • Functions • gets • syntax #include<stdio.h> • char *gets(char *s) • char string[10]; • gets(string); • The function gets reads one character at a time from the input stream until a carriage return is encountered. • It does not include \n character, but puts in a null \0 to signal the end of the string.
Strings Output 1234 67890 |1234| |67890| 1234 67890 |1234 67890| 67890 | 67890| You may press Enter to bye Example : #include <stdio.h> void main() { char s1[20],s2[20]; scanf(“%s %s”,s1,s2); printf(“|%s|\n”,s1); printf(“|%s|\n”,s2); fflush(stdin); gets (s1); printf(“|%s|\n”,s1); fflush(stdin); gets (s2); printf(“|%s|\n”,s2); printf(“You may press Enter to bye\n”); fflush(stdin); getchar(); }
Strings.h
Character Array (activity) • For each value, declare a variable in C and initialize the variables : • i) ABC (character array only and not string) • ii) 30 Good Shepherd St.
Array (activity) • For each value, declare a variable in C and initialize the variables : • i) ABC (character array only and not string) • char aString[] ={‘A’, ‘B’, ‘C’}; • ii) 30 Good Shepherd St. • char aString[] = “30 Good Shepherd St. “;
The basics of I/O • Input to a C program • A sequence of data bytes coming in. • Output to a C program • A sequence of data bytes going out.
Data hierarchy • bit 0 • byte 01000001 (ASCII character of ‘A’) • 28 = 256 (possible values) • field • record • file • database
Data Streams • Standard input stream • int getchar(void); • Standard out stream • int putchar(int c); • Standard error stream
Buffering Program Buffer Keyboard standard input
File manipulation • A record is represented in C by structure. • A file that is a group of logically related records is called a data file.
Text files • A text file is a collection of characters saved in the secondary storage and has no fixed size. • The computer places a special <eof> end-of-file character to mark the end of file. • Each separate line ends with a <newline> character. • You can create and edit a text file using an editor program.
File pointer variable • Declare file pointer variables. • FILE* infile; • FILE* outfile;
Open a file • File Acess modes • r open for read only • w open for write only (if the file exists, it will be overwritten) • a open for append, i.e. adding to the EOF, if the file exists
Establishing a data file • File* output; • if ( (outfile = fopen(“a:\sample.dat”. “w”) = = NULL) { • printf(“Output File cannot be opened.\n”); • return 1; • }
Common I/O functions concerning characters
Functions that access user-defined files • ch = getc(infile); • putc(ch, outfile); • fgets(buffer, BUFFERLEN, infile); • fputs(buffer, outfile); • fscanf(infile, “%d”, &no); • fprintf(outfile, “OUHK”); • rewind(infile);
Closing a file • fclose(infile); • fclose(output);
Examples • #include <stdio.h> • int main() { • int data; • FILE* fpInput; • FILE* fpOutput; • fpInput = fopen(“InputOutput2.c”, “r”); • fpOutput = fopen(“InputOutput2.bak”, “w”); • if (fpInput == NULL || fpOutput == NULL) { • printf(“Output File cannot be opened.\n”); • return 1; • } • while ((data = getc(fpInput)) != EOF) { • putc(data, fpOutput); • } • fclose(fpInput); • fclose(fpOutput); • getchar(); /* to hold the screen */ • return 0; • }
Activity • State the syntax and logical errors for the following program for reading a line of lower-case text from the standard input and then store its upper-case equivalent. • #include <stdio.h> • void main() • { • file *fpt; • char c; • fpt = fopen("sample.dat", "r"); • do • putc(toupper(c = getchar()), *fpt); • while (c != '\n'); • fclose (fpt); • }
Activity • FILE *fpt; FILE must be upper case. • fpt = fopen("sample.dat", "w"); use "w" mode for output purpose. • putc(toupper(c = getchar()), fpt); fpt is a FILE pointer already, no asterisk is required.
Common escape sequences
Conversion characters for formatted output
Examples • #include <stdio.h> • #include <math.h> • int main(){ • double x = sin(15); • printf(“|%f|\n”, x); |0.650288| • printf(“|%10f|\n”, x); | 0.650288| • printf(“|%.10f|\n”, x); |0.6502878402| • printf(“|%-10f|\n”, x); |0.650288 | • printf(“|%.20f|\n”, x); |0.65028784015711682540| • printf(“|%-20f|\n”, x); |0.650288 | • printf(“|%20.10f|\n”, x); | 0.6502878402| • printf(“|%-20.10f|\n”, x); |0.6502878402 | Press ‘Enter’ to continue. • printf(“Press ‘Enter’ to continue.\n”); Press ‘Enter’ to continue. • getchar(); • }
Conversion characters for formatted input
