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EKT120 COMPUTER PROGRAMMING

EKT120 COMPUTER PROGRAMMING. Arrays & Strings (Part II) Dr. Nik Adilah Hanin Bt. Zahri adilahhanin@unimap.edu.my. Recaps… What is Array?. An array is a collection of a fixed number of components wherein all of the components are of the same type

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EKT120 COMPUTER PROGRAMMING

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  1. EKT120COMPUTER PROGRAMMING Arrays & Strings (Part II) Dr. NikAdilahHanin Bt. Zahri adilahhanin@unimap.edu.my

  2. Recaps… What is Array? • An array is a collection of a fixed number of components wherein all of the components are of the same type • Example: Suppose that there is a list of five integers: 5, 10, 15, 20, and 25 • Previously we would declare five variables: int iNum1,iNum2,iNum3,iNum4,iNum5; • By using array, since they are all of the same data type, we could just write: intaiNum[5];

  3. Recaps… What is Array? aiNum • intaiNum[5]; • 5 components or elements in this array • Elements are referred to index • Element aiNum[2] has index 2 and value 15 aiNum[0] aiNum[1] aiNum[2] aiNum[3] aiNum[4]

  4. Recaps… 2-Dimensional Array intaiValue[4][2]; aiValue[2][1]=5; Column 0 1 0 1 2 3 Row

  5. Recaps… 2-Dimensional Array intaiValue[4][2]; aiValue[2][1]=5; Column 0 1 0 1 2 3 Row

  6. Outline • Introduction to Strings • Declaration of Strings • Fundamentals of Strings & Characters • Initialization of Strings • Assigning Values to Strings • Character and String Manipulations • Strings Conversion Functions • ASCII Table

  7. What is a String? • A string is a series of characters treated as a single unit. • Also known as character array • Strings can be treated as array of type char used to store names of people, places, or anything that involves a combination of letters. • A string may include letters, digits and various special characters such as +, -, *, ? and $. • String literals, or string constants, in C are written in double quotation marks ( “ ” ) as follows: Example: “John Doe” (a name) “99999 Main Street” (a street address) “Kangar, Perlis” (a city and a state) “(012) 123-8755” (a telephone number)

  8. What is a String? • The data type string is a programmer-defined and is not part of the C language • A string with no characters is called a null or empty string. “ ” is the empty string. • Every character in a string has a relative position in the string. • The position of the first character is 0, position of the second is 1, and so on. • The length of a string is the number of character in it. of a string is the address of its first character.

  9. Example String Position of a Character Length of the String in the String “William Jacob” Position of ‘W’ is 0 13 Position of the first ‘i’ is 1 Position of ‘ ’ (the space) is 7 Position of ‘J’ is 8 Position of ‘b’ is 12 “Mickey” Position of ‘M’ is 0 6 Position of ‘i’ is 1 Position of ‘c’ is 2 Position of ‘k’ is 3 Position of ‘e’ is 4 Position of ‘y’ is 5

  10. Declaration of Strings • Declaration of string/character array char variable_name[length]; • An example of declaration of an array (or string of characters): char name[10]; //declaration • can use to store “William”, “John Doe” etc and all strings that shorter than defined length • It is not necessary that this max size of 10 characters should at all the times fully used • The last value in the string will be a null character (‘\0’). char name[10]; can store a string up to 10 characters long, and may visualize it as below name

  11. Declaration of Strings (cont…) • name is an array of 10 elements of type char,could be represented by storing the strings of characters, e.g. “William” and “John Doe” in the following way: name W i l l i a m \0 to indicate end of string indefinite values J o h n D o e \0

  12. Declaration of Strings (cont…) • Also can be declared as a character array or a variable of type char * char name[] = “William"; char *name = “William";

  13. Formatted Input/ Output • Formatted input • Use scanf scanf("%s", name); • Copies input into name[] • Does not need & (because a string is a pointer) • Remember to leave room in the array for the null character ('\0’) • Formatted output • Use printf printf(“%s”,name);

  14. Example : Input and Output of String • Input and output characters using scanf() andprintf() • Example program: #include<stdio.h> int main() { char name[30]; printf("Enter name: "); scanf(“%s”,name); //read string from user printf(“Hi %s\n“,name); //display string return 0; }

  15. Initialization of String • Similar to array, but each character is enclosed in ‘ ’ or “ ”. • Example: • char newString[]={‘W’, ‘e’, ‘l’, ‘c’, ‘o’, ‘m’, ‘e’, ‘\0’}; • char newString[]= “Welcome”; • ‘\0’ is automatically inserted • The difference is that single quotes (‘) are used to specify single character constants and null character must be added at the end of the sentence. char newString[]= {‘W’,‘e’,‘l’,‘c’,‘o’,‘m’,‘e’,‘\0’}; Single quotes – null char must be added

  16. Initialization of String • On the other hand, double quotes (“) are constant that specify sequence of characters andalways have a null character (‘\0’) automatically inserted at the end. char newString[] = “Welcome”; Double quotes – null char automatically inserted

  17. Initialization of String (cont…) • The examples below are NOT VALIDfor string / characters array. newString = “Welcome”; //no [] and data type newString [] =“Welcome”; //no data type newString = {‘W’,‘e’,‘l’,‘c’,‘o’,‘m’,‘e’,‘\0’}; //no [] and data type

  18. Assigning Values to String • The left hand side value of an assignation can only be array items and not the entire array, a possible way to assign a string of characters to an array of charcan be shown as: newString[0] = ‘W’; newString[1] = ‘e’; newString[2] = ‘l’; newString[3] = ‘c’; newString[4] = ‘o’; newString[5] = ‘m’; newString[6] = ‘e’; newString[7] = ‘\0’;

  19. Character and String Manipulation • A program may need to verify/perform, e.g. • Calculation of the string size • Copy one string to another • Appends one string to another • Built-in functions available – makes it easier. • Standard input/output library <stdio.h> • General utilities library <stdlib.h> • Character handling library <ctype.h> • String handling library <string.h>

  20. Example 1: Input and Output of String • Input and output characters using gets() puts() function from <stdio.h> • Example program: #include<stdio.h> int main() { char name[30]; printf("Enter name: "); gets(name); //Function to read string from user printf(“Hi "); puts(name); //Function to display string return 0; }

  21. Example 1: Input and Output of String • Input and output characters using gets() puts() function from <stdio.h> • Example program: #include<stdio.h> int main() { char name[30]; printf("Enter name: "); gets(name); //Function to read string from user printf(“Hi "); puts(name); //Function to display string return 0; } Enter name : John Hi John

  22. Example 2: Input and Output of String • Input and output characters using gets() puts() function from <stdio.h> • Example program: #include<stdio.h> int main() { char name[3][30]; printf("Enter 3 names:\n"); for(i=0;i<3;i++) gets(name[i]); //Function to read string from user printf(“\nName Entered:\n”); for(i=0;i<3;i++) puts(name[i]); //Function to display string return 0; }

  23. Example 2: Input and Output of String • Input and output characters using gets() puts() function from <stdio.h> • Example program: #include<stdio.h> int main() { char name[3][30]; printf("Enter 3 names:\n"); for(i=0;i<3;i++) gets(name[i]); //Function to read string from user printf(“\nName Entered:\n”); for(i=0;i<3;i++) puts(name[i]); //Function to display string return 0; } Enter 3 names: Michael John Sarah Names Entered: Michael John Sarah

  24. Example 3: Calculation of String Size • Calculation of string size using strlen(char *string)function from <string.h> • char is 1 byte, the total number of alphabets would be the size of the string. • Example program: #include <stdio.h> #include <string.h> char newString1[] = {'W','e','l','c','o','m','e','\0'}; char newString2[] = "Good Bye"; int main() { //size of string Welcome printf ("Size of ‘%s’ is %d\n", newString1,strlen(newString1); //size of string Good Bye printf ("\nSize of ‘%s’ is %d\n",newString2,strlen(newString2)); return 0; }

  25. Example 3: Calculation of String Size • Calculation of string size using strlen(char *string)function from <string.h> • char is 1 byte, the total number of alphabets would be the size of the string. • Example program: #include <stdio.h> #include <string.h> char newString1[] = {'W','e','l','c','o','m','e','\0'}; char newString2[] = "Good Bye"; int main() { //size of string Welcome printf ("Size of ‘%s’ is %d\n", newString1,strlen(newString1); //size of string Good Bye printf ("\nSize of ‘%s’ is %d\n",newString2,strlen(newString2)); return 0; } Size of `Welcome’ is 7 Size of `Good Bye’ is 8

  26. Example 4: Controlling Case of a Character • In C, upper case letter, e.g. ‘K’ is not equal to lower case ‘k’ • So in C programming, you usually use: if (cChoice == ‘K’ || cChoice == ‘k’), OR while (cChoice == ‘Y’ || cChoice == ‘y’) • The case of a character can be controlled using tolower() and toupper() functions from <ctype.h> • temporarily converts a letter/char to uppercase or lowercase before comparing it toupper(int c) tolower(int c) • Also, can use functions that converts the whole string to upper or lowercase from <string.h> strupr(char *string) strlwr(char *string)

  27. Example 4: Controlling Case of a Character … char cChoice; printf ( “Continue? (Y or N) : “); scanf (“%c”, &cChoice); while(tolower(choice)=='y') { … … scanf("%s",&choice); } …

  28. Example 5: Controlling Case of a Character //To convert a string to uppercase #include <stdio.h> #include <string.h> void main() { char acName[20]; //declare an array of //characters 0-79 printf("Enter in a name in lowercase\n"); scanf( "%s", acName ); strupr(acName); printf("The name in uppercase is %s", acName ); }

  29. Example 5: Controlling Case of a Character //To convert a string to uppercase #include <stdio.h> #include <string.h> void main() { char acName[20]; //declare an array of //characters 0-79 printf("Enter in a name in lowercase\n"); scanf( "%s", acName ); strupr(acName); printf("The name in uppercase is %s", acName ); } Enter in a name in lowercase john The name in uppercase is JOHN

  30. Example 6: Controlling Case of a Character //To convert a string to uppercase #include <stdio.h> #include <ctype.h> int main() { inti=0; char line[]= "my NAME is JOHN"; printf(“Before conversion : %s\n",line); i=0; while (line[i] != 0) { if (islower(line[i])) { line[i]= toupper(line[i]); } ++i; } printf(“After conversion : %s\n",line); return 0; }

  31. Example 6: Controlling Case of a Character //To convert a string to uppercase #include <stdio.h> #include <ctype.h> int main() { inti=0; char line[]= "my NAME is JOHN"; printf(“Before conversion : %s\n",line); i=0; while (line[i] != 0) { if (islower(line[i])) { line[i]= toupper(line[i]); } ++i; } printf(“After conversion : %s\n",line); return 0; } Before conversion : my NAME is JOHN After conversion : MY NAME IS JOHN

  32. Example 7: Controlling Case of a Character void changeCase1(char *strPtr) { while (*strPtr!= NULL) { if (islower(*strPtr)) *strPtr= toupper(*strPtr); ++strPtr; } } • void changeCase2(char *strPtr) • { • for(;*strPtr!= NULL;strPtr++) • { • if (isupper(*strPtr)) • *strPtr= tolower(*strPtr); • } • } #include <stdio.h> #include <ctype.h> void changeCase1(char *strPtr); void changeCase1(char *strPtr); int main() { char string[] = “my NAME is JOHN"; printf(“Before conversion: %s\n",string); changeCase1(string); printf(“After conversion1: %s\n",string); changeCase2(string); printf(“After conversion2: %s\n",string); return 0; }

  33. Example 7: Controlling Case of a Character void changeCase1(char *strPtr) { while (*strPtr!= NULL) { if (islower(*strPtr)) *strPtr= toupper(*strPtr); ++strPtr; } } • void changeCase2(char *strPtr) • { • for(;*strPtr!= NULL;strPtr++) • { • if (isupper(*strPtr)) • *strPtr= tolower(*strPtr); • } • } #include <stdio.h> #include <ctype.h> void changeCase1(char *strPtr); void changeCase1(char *strPtr); int main() { char string[] = “my NAME is JOHN"; printf(“Before conversion: %s\n",string); changeCase1(string); printf(“After conversion1: %s\n",string); changeCase2(string); printf(“After conversion2: %s\n",string); return 0; } Before conversion : my NAME is JOHN After conversion1 : MY NAME IS JOHN After conversion2 : my name is john

  34. Controlling Case of a Character • Real value does not changed. • The functions only affect characters of letters or alphabets. • does not affect numbers and special characters such as $ and % • If the character is already lowercase or uppercase, the function will not affect the real value • return the original value Example: char cRepeat = ‘Y’; cLetter = strupr(cRepeat); cLetter = ?

  35. Strings Conversion Functions • Conversion functions • In <stdlib.h>(general utilities library) • Convert strings of digits to integer and floating-point values

  36. Strings Comparison Functions • Comparing strings • Computer compares numeric ASCII codes of characters in string intstrcmp( const char *s1, const char *s2 ); • Compares string s1 to s2 • Returns a negative number if s1 < s2, zero if s1 == s2 or a positive number if s1 > s2 intstrncmp(const char *s1, const char *s2, size_t n ); • Compares up to n characters of string s1 to s2 • Returns values as above

  37. ASCII Table ‘A’  65, ‘a’  97

  38. Sample Program 1 #include <stdio.h> #include <string.h> int main() { char acString1[20], acString2[20]; //declaration intiResult; printf( "Enter two strings: " ); scanf( "%s %s", acString1, acString2 ); iResult = strcmp( acString1, acString2);//comparing acString1 and acString2 if (iResult > 0 ) printf( "\"%s\" is greater than \"%s\"\n",acString1, acString2 ); else if ( iResult == 0 ) printf( "\"%s\" is equal to \"%s\"\n",acString1, acString2 ); else printf( "\"%s\" is less than \"%s\"\n",acString1, acString2 ); return 0; }

  39. Sample Program 1 #include <stdio.h> #include <string.h> int main() { char acString1[20], acString2[20]; //declaration intiResult; printf( "Enter two strings: " ); scanf( "%s %s", acString1, acString2 ); iResult = strcmp( acString1, acString2 );//comparing acString1 and acString2 if ( iResult > 0 ) printf( "\"%s\" is greater than \"%s\"\n",acString1, acString2 ); else if ( iResult == 0 ) printf( "\"%s\" is equal to \"%s\"\n",acString1, acString2 ); else printf( "\"%s\" is less than \"%s\"\n",acString1, acString2 ); return 0; } Enter two strings: computer programming "computer" is less than "programming" Enter two strings: programming computer "programming" is greater than "computer"

  40. Sample Program 2 #include <stdio.h> #include <string.h> int main() { char acString1[ 20 ], acString2[ 20 ]; intiResult, iCompareCount; printf( "Enter two strings: " ); scanf( "%s %s", acString1, acString2 ); printf( "How many characters should be compared: " ); scanf( "%d", &iCompareCount ); iResult = strncmp( acString1, acString2, iCompareCount ); if (iResult > 0 ) printf( "\"%s\" is greater than \"%s\" up to %d characters\n", acString1, acString2, iCompareCount ); else if ( iResult == 0 ) printf( "\"%s\" is equal to \"%s\" up to %d characters\n", acString1, acString2, iCompareCount ); else printf( "\"%s\" is less than \"%s\" up to %d characters\n", acString1, acString2, iCompareCount ); return 0; }

  41. Sample Program 2 #include <stdio.h> #include <string.h> int main() { char acString1[ 20 ], acString2[ 20 ]; intiResult, iCompareCount; printf( "Enter two strings: " ); scanf( "%s %s", acString1, acString2 ); printf( "How many characters should be compared: " ); scanf( "%d", &iCompareCount ); iResult = strncmp( acString1, acString2, iCompareCount ); if (iResult > 0 ) printf( "\"%s\" is greater than \"%s\" up to %d characters\n", acString1, acString2, iCompareCount ); else if ( iResult == 0 ) printf( "\"%s\" is equal to \"%s\" up to %d characters\n", acString1, acString2, iCompareCount ); else printf( "\"%s\" is less than \"%s\" up to %d characters\n", acString1, acString2, iCompareCount ); return 0; } Enter two strings: computer programming How many characters should be compared: 7 "computer" is less than "programming" up to 7 characters Enter two strings: programming computer How many characters should be compared: 7 "programming" is greater than "computer" up to 7 characters

  42. Built in Functions for String Handling • strcat Appends a string • strchr Finds first occurrence of a given character • strcmp Compares two strings • strcmpi Compares two strings, non-case sensitive • strcpy Copies one string to another • strlen Finds length of a string • strlwr Converts a string to lowercase • strncat Appends n characters of string • strncmp Compares n characters of two strings • strncpy Copies n characters of one string to another • strnset Sets n characters of string to a given character • strrchr Finds last occurrence of given character in string • strrev Reverses string • strset Sets all characters of string to a given character • strspn Finds first substring from given character set in string • strupr Converts string to uppercase

  43. End – Arrays & Strings Q & A!

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