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Lecture 8 – Arrays (2) and Strings

Lecture 8 – Arrays (2) and Strings. Outline. 8.1 Passing Arrays to Function 8.2 Displaying Array in a Function 8.3 How Arrays are passed in a function call 8.4 Introduction to Strings 8.5 Strings Type 8.6 Character Array 8.7 Declaration of Strings 8.8 Fundamentals of Strings & Characters

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Lecture 8 – Arrays (2) and Strings

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  1. Lecture 8 – Arrays (2) and Strings PGT 106 - C Programming

  2. Outline 8.1 Passing Arrays to Function 8.2 Displaying Array in a Function 8.3 How Arrays are passed in a function call 8.4 Introduction to Strings 8.5 Strings Type 8.6 Character Array 8.7 Declaration of Strings 8.8 Fundamentals of Strings & Characters 8.9 Initialization of Strings 8.10 Assigning Values to Strings 8.11 Calculation of Strings Size 8.12 Strings Conversion Functions 8.13 Comparison Functions of the Strings 8.14 ASCII Table PGT 106 - C Programming

  3. Passing Arrays to Function void fnInitialize (int aiList [ ]) { int iCount; for (iCount = 0; iCount < 5; iCount ++) aiList [iCount] = 0; } • Initializes int array of size 5 to 0. PGT 106 - C Programming

  4. Array as Parameter in Function • If size changes (lets say 10 or 20), need to write another function.  not practical and inflexible. • Therefore, introduce another variable, iSize. void fnInitialize (int aiList [ ], int iSize) { int iCount; for (iCount = 0; iCount < iSize; iCount ++) aiList [iCount] = 0; } PGT 106 - C Programming

  5. Constant Arrays • Prevent the function from changing the values in array. • Use word const in declaration. • Function can modify array aiX but not array aiY. void fnExample (int aiX[ ], const int aiY[ ], int iSizeX[ ],int iSizeY[ ]) { ….. ….. …. …. } PGT 106 - C Programming

  6. Initialize an array to 0 void fnInitializeArray (int aiX[ ], int iSizeX) { int iCounter; for (iCounter = 0; iCounter < iSizeX; iCounter ++) aiX [iCounter] = 0; } PGT 106 - C Programming

  7. Read data and store it in an array void fnFillArray (int aiX[ ], int iSizeX) { int iCounter; for (iCounter = 0; iCounter < iSizeX; iCounter++) scanf (“%d”, &aiX [iCounter]); } PGT 106 - C Programming

  8. Displaying array in a function void fnPrintArray (const int aiX[ ], int iSizeX) { int iCounter; for (iCounter = 0; iCounter < iSizeX; iCounter ++) printf (“%d”, aiX [iCounter]); } PGT 106 - C Programming

  9. Find and return the sum of an array int fnSumArray (const int aiX[ ], int iSizeX) { int iCounter; int iSum = 0; for (iCounter = 0; iCounter < iSizeX; iCounter ++) iSum = iSum + aiX[iCounter]; return iSum; } PGT 106 - C Programming

  10. Find and return index of largest element of an array int fnIndexLargestElement (const int aiX[ ], int iSizeX) { int iCounter; int iMaxIndex = 0; for (iCounter = 0; iCounter < iSizeX; iCounter ++) if ( aiX[iMaxIndex] < aiX[iCounter] ) iMaxIndex = iCounter; return iMaxIndex; } PGT 106 - C Programming

  11. Copy an array into another array void fnCopyArray (const int aiX[ ], int aiY[ ], int iLength) { int iCounter; for (iCounter = 0; iCounter < iLength; iCounter ++) aiY[iCounter] = aiX[iCounter]; } PGT 106 - C Programming

  12. How arrays are passed in a function call #include <stdio.h> const int iArraySize = 10; void fnInitializeArray (int aiX[], int iSizeX); void fnFillArray (int aiX[], int iSizeX); void fnPrintArray (const int aiX[], int iSizeX); int fnSumArray (const int aiX[], int iSizeX); int fnIndexLargestElement (const int aiX[], int iSizeX); void fnCopyArray (const int aiX[], int aiY[], int iLength); PGT 106 - C Programming

  13. How arrays are passed in a function call int main() { int aiListA [iArraySize] = {0}; int aiListB [iArraySize]; fnPrintArray (aiListA, iArraySize); fnInitializeArray (aiListB, iArraySize); fnPrintArray (aiListB, iArraySize); fnFillArray (aiListA, iArraySize); fnPrintArray (aiListA, iArraySize); fnSumArray (aiListA, iArraySize); fnCopyArray (aiListA, aiListB, iArraySize); fnPrintArray (aiListB, iArraySize); return 0; } PGT 106 - C Programming

  14. Sample Program #include <stdio.h> void fnPrintArray (const int aiA[][3]); // function prototype //function main begins program execution int main() { //initialize array1, array2, array3 int aiArray1 [2][3] = { {1, 2, 3}, {4, 5, 6} }; int aiArray2 [2][3] = { 1, 2, 3, 4, 5 }; int aiArray3 [2][3] = { {1, 2 }, { 4 } }; printf (“Values in array1 by row are : \n); fnPrintArray (aiArray1); printf ("Values in array2 by row are : \n"); fnPrintArray (aiArray2); printf ("Values in array3 by row are : \n"); fnPrintArray (aiArray3); return 0; } // end of main PGT 106 - C Programming

  15. Sample Program (cont…) //function to display array with two rows and three columns void fnPrintArray (const int aiA[][3]) { int iRow; //row counter int iColumn; //column counter //loop through row for (iRow = 0; iRow <= 1; iRow++) { //output column values for (iColumn = 0; iColumn <= 2; iColumn++) { printf ("%d ", aiA[iRow][iColumn]); } //end inner for printf ("\n"); //start new line of output } //end outer for } //end function fnPrintArray PGT 106 - C Programming

  16. Sample Program (cont…) Output Values in array1 by row are : 1 2 3 4 5 6 Values in array2 by row are : 1 2 3 4 5 0 Values in array3 by row are : 1 2 0 4 0 0 PGT 106 - C Programming

  17. What is a String? • A string is a series of characters treated as a single unit. • 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: “John Doe” (a name) “99999 Main Street” (a street address) “Kangar, Perlis” (a city and a state) “(012) 123-8755” (a telephone number) PGT 106 - C Programming

  18. What is a String? • The data type string is a programmer-defined and is not part of the C language. The C standard library supplies it. • 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. • A string is accessed via a pointer to the first character in the string. • The value of a string is the address of its first character. PGT 106 - C Programming

  19. 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 PGT 106 - C Programming

  20. String Type • To use the data type string, the program must include the header file string. #include <string.h> • The statement string acInfo = “Welcome”; declares acInfo to be string variable and also initializes info to “Welcome”. • The position of the first character, ‘W’, in the acinfo is 0, the position of the second character, ‘e’, is 1, and so on. • The variable acInfo is capable of storing (just about) any size string. PGT 106 - C Programming

  21. Character Array (string of characters) • char acInfo [10]; • Can store “Welcome”, “Good Bye”. • char acName [50]; • Able to store shorter strings than total length. • The last value in the string will be a null character (‘\0’). PGT 106 - C Programming

  22. Declaration of Strings • An example of declaration of an array (or string of characters): • It is not necessary that this max size of 10 characters should at all the times be fully used. acInfo could store at any part of the program either the string of characters “Welcome” or the string “Good Bye”. char acInfo [10]; can store a string up to 10 characters long, and may visualize it as below acInfo PGT 106 - C Programming

  23. Declaration of Strings (cont..) • A null character, constant 0 or ‘\0’ can be written at the end of the valid content of a string if the characters to be stored is shorter than its total length (10 in this case). • acInfo is an array of 10 elements of type char,could be represented by storing the strings of characters “Welcome” and “Good Bye” in the following way: PGT 106 - C Programming

  24. Declaration of Strings (cont..) acInfo W e l c o m e \0 to indicate end of string indefinite values G O o d B y e \0 PGT 106 - C Programming

  25. Fundamentals of Strings and Characters • String declarations • Declare as a character array or a variable of type char * char acInfo[] = “Welcome"; char *pcInfo = “Welcome"; • Remember that strings represented as character arrays end with '\0' • acInfo has 8 elements • Inputting strings • Use scanf scanf("%s", acWord); • Copies input into acWord[] • Does not need & (because a string is a pointer (slide 18)) • Remember to leave room in the array for the null character ('\0’) PGT 106 - C Programming

  26. Initialization of string • Similar to array, but each character is enclosed in ‘ ’ or “ ”. • Example: • char acNewString[]={‘W’, ‘e’, ‘l’, ‘c’, ‘o’, ‘m’, ‘e’, ‘\0’}; • char acNewString[]= “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. PGT 106 - C Programming

  27. Initialization of string (cont…) • 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 acNewString[]= {‘W’,‘e’,‘l’,‘c’,‘o’,‘m’,‘e’,‘\0’}; char acNewString[] = “Welcome”; Single quotes – null char must be added Double quotes – null char automatically inserted PGT 106 - C Programming

  28. Initialization of string (cont…) • The examples below are not valid for string of 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 PGT 106 - C Programming

  29. 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 char can be shown as: acNewString[0] = ‘W’; acNewString [1] = ‘e’; acNewString [2] = ‘l’; acNewString [3] = ‘c’; acNewString [4] = ‘o’; acNewString [5] = ‘m’; acNewString [6] = ‘e’; acNewString [7] = ‘\0’; PGT 106 - C Programming

  30. Calculation of string size • char is 1 byte, the total number of alphabets plus a null would be the size of the string. Example program: #include <stdio.h> #include <string.h> char acNewString[] = {'W','e','l','c','o','m','e','\0'}; char acMyString[] = "Good Bye"; int main() { printf ("Size of acNewString is %d", sizeof (acNewString)); //size of string Welcome printf ("\nSize of acMyString is %d", sizeof (acMyString));// size of string Good Bye return 0; } What is the output? PGT 106 - C Programming

  31. Character and string manipulation • Examples: • a program may need to verify that an ID number of first year students starts with ‘09’. • determine whether last three characters in a part number are valid. • Built-in functions available – makes it easier. PGT 106 - C Programming

  32. Controlling the case of a character • ‘K’ is not equal to ‘k’. • You use: if (cChoice == ‘K’ || cChoice == ‘k’) while (cChoice == ‘Y’ || cChoice == ‘y’) • Can use a function that temporarily converts the letter to uppercase or lowercase before comparing it. strupr(charVariable) strlwr(charVariable) PGT 106 - C Programming

  33. Controlling the case of a character (Example) char cChoice; printf ( “Continue? (Y or N) : “); scanf (“%c”, &cChoice); while (strupr(cChoice) == ‘Y’) { ….. ….. ….. } PGT 106 - C Programming

  34. Controlling the case of a character (Example) char acName[]; printf (“Enter a name : “); scanf (“%s”, acName); strupr(acName); printf("The name in uppercase is %s", acName ); PGT 106 - C Programming

  35. Sample Program 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 ); } Output Enter in a name in lowercase john The name in uppercase is JOHN PGT 106 - C Programming

  36. Controlling the 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. It will return the original value. char cRepeat = ‘Y’; cLetter = strupr(cRepeat); • cLetter = ? PGT 106 - C Programming

  37. Strings Conversion Functions • Conversion functions • In <stdlib.h> (general utilities library) • Convert strings of digits to integer and floating-point values PGT 106 - C Programming

  38. Strings Comparison Functions • 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, zero if s1 == s2 or a positive 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 PGT 106 - C Programming

  39. ASCII Table PGT 106 - C Programming

  40. Sample Program 1 #include <stdio.h> #include <string.h> int main() { char acString1[ 20 ], acString2[ 20 ]; //declaration of acString1 and acString2 int iResult; printf( "Enter two strings: " ); scanf( "%s %s", acString1, acString2 ); iResult = strcmp( acString1, acString2 ); //compare between 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; } PGT 106 - C Programming

  41. Sample Program 1 (cont…) • Output Enter two strings: computer programming "computer" is less than "programming" Enter two strings: programming computer "programming" is greater than "computer" PGT 106 - C Programming

  42. Sample Program 2 #include <stdio.h> #include <string.h> 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; } PGT 106 - C Programming

  43. Sample Program 2 (cont…) Output 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 PGT 106 - C Programming

  44. 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 • strnca t 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 PGT 106 - C Programming

  45. End – Arrays (2) & Strings Q & A! PGT 106 - C Programming

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