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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: int aiNum[5]; 2

aiNum aiNum[0] aiNum[1] aiNum[2] aiNum[3] aiNum[4] int aiNum[5]; 5 components or elements in this array Elements are referred to index Element aiNum[2] has index 2 and value 15

Column aiValue[0][0]aiValue[0][1] aiValue[1][0]aiValue[1][1] aiValue[2][0]aiValue[2][1] aiValue[3][0]aiValue[3][1] Row int aiValue[4][2]; aiValue[2][1]=5;

Column aiValue[0][0]aiValue[0][1] aiValue[1][0]aiValue[1][1] aiValue[2][0]5 aiValue[3][0]aiValue[3][1] Row int aiValue[4][2]; aiValue[2][1]=5;

1. Introduction to Strings 2. Declaration of Strings 3. Fundamentals of Strings & Characters 4. Initialization of Strings 5. Assigning Values to Strings 6. Character and String Manipulations 7. Strings Conversion Functions 8. ASCII Table 6

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) ”(a telephone number) 7

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. 8

StringPosition of a CharacterLength of the String in the String “William Jacob”Position of ‘W’ is 013 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 06 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 9

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’). 10 name char name[10]; can store a string up to 10 characters long, and may visualize it as below

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: 11 W name illiam\0 JeoDnho to indicate end of string indefinite values

Also can be declared as a character array or a variable of type char * char name[] = “William"; char *name = “William"; 12

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); 13

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

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’}; 15 Single quotes – null char must be added

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

The examples below are NOT VALID for 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 17

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 char can 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’; 18

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 General utilities library Character handling library String handling library 19

#include 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; } Input and output characters using gets() puts() function from Example program: 20

#include 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; } Input and output characters using gets() puts() function from Example program: 21 Enter name : John Hi John

#include 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; } Input and output characters using gets() puts() function from Example program: 22

#include 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; } Input and output characters using gets() puts() function from Example program: 23 Enter 3 names: Michael John Sarah Names Entered: Michael John Sarah

Calculation of string size using strlen(char *string) function from char is 1 byte, the total number of alphabets would be the size of the string. Example program: #include 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; } 24

Calculation of string size using strlen(char *string) function from char is 1 byte, the total number of alphabets would be the size of the string. Example program: #include 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 Size of `Welcome’ is 7 Size of `Good Bye’ is 8

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 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 strupr(char *string) strlwr(char *string) 26

… char cChoice; printf ( “Continue? (Y or N) : “); scanf (“%c”, &cChoice); while(tolower(choice)=='y') { … scanf("%s",&choice); } … 27

//To convert a string to uppercase #include 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 ); } 28

//To convert a string to uppercase #include 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 Enter in a name in lowercase john The name in uppercase is JOHN

//To convert a string to uppercase #include int main() { int i=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; } 30

//To convert a string to uppercase #include int main() { int i=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 Before conversion : my NAME is JOHN After conversion : MY NAME IS JOHN

32 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 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 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 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

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 = ? 34

Conversion functions In (general utilities library) Convert strings of digits to integer and floating-point values 35

Comparing strings Computer compares numeric ASCII codes of characters in string int strcmp( const char *s1, const char *s2 ); Compares string s1 to s2 Returns a negative number if s1 s2 int strncmp(const char *s1, const char *s2, size_t n ); Compares up to n characters of string s1 to s2 Returns values as above 36

ASCII Character Set nulsohstxetxeotenqackbelbsht 1Ifvtffcrsosidledc1dc2dc3 2dc4naksynetbcanemsubescfsgs 3rsussp!“#$%&` 4()*+,-./ :; 7FGHIJKLMNO 8PQRSTUVWXY 9Z[\]^_’abC 10defghijklM 11nopqrstUvW 12xyz{|}~del 37 ‘A’  65, ‘a’  97

#include int main() { char acString1[20], acString2[20]; //declaration int iResult; 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; } 38

#include int main() { char acString1[20], acString2[20]; //declaration int iResult; 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 Enter two strings: computer programming "computer" is less than "programming" Enter two strings: programming computer "programming" is greater than "computer"

#include int main() { char acString1[ 20 ], acString2[ 20 ]; int iResult, 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; } 40

41 #include int main() { char acString1[ 20 ], acString2[ 20 ]; int iResult, 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

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 strncatAppends 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 42

Q & A! 43