Fundamentals of Programming Session 22 Instructor: Reza - PowerPoint PPT Presentation

Fundamentals of Programming Session 22 Instructor: Reza Entezari-Maleki Email: entezari@ce.sharif.edu 1 Fall 2014 These slides have been created using Deitel’s slides Sharif University of Technology

Outlines  Relationship between Pointers and Arrays  Arrays of Pointers  Fundamentals of Strings and Characters 2

Relationship between Pointers and Arrays  Pointers can be used to do any operation involving array subscripting.  Assume that integer array b[5] and integer pointer variable bPtr have been defined.  Since the array name (without a subscript) is a pointer to the first element of the array, we can set bPtr equal to the address of the first element in array b with the statement  bPtr = b;  This statement is equivalent to taking the address of the array’s first element as follows:  bPtr = &b[ 0 ]; ];  Array element b[3] can alternatively be referenced with the pointer expression  *( bPtr + 3 )  The preceding notation is referred to as pointer/offset notation. 3

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Relationship between Pointers and Arrays …  To further illustrate the interchangeability of arrays and pointers, let’s look at the two string-copying functions — copy1 and copy2 — in the program of Fig. 7.21.  Both functions copy a string (possibly a character array) into a character array.  After a comparison of the function prototypes for copy1 and copy2 , the functions appear identical. they’re  They accomplish the same task; however, implemented differently. 7

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Arrays of Pointers  Arrays may contain pointers.  A common use of an array of pointers is to form an array of strings, referred to simply as a string array.  Each entry in the array is a string, but in C a string is essentially a pointer to its first character.  So each entry in an array of strings is actually a pointer to the first character of a string.  Consider the definition of string array suit , which might be useful in representing a deck of cards.  const char const char *suit[ *suit[ 4 ] = { ] = { "Hearts" "Hearts", , "Diamonds" "Diamonds", , "Clubs" "Clubs", , "Spades" "Spades" }; }; 10

Arrays of Pointers …  The four strings are 7, 9, 6 and 7 characters long, respectively.  Although it appears as though these strings are being placed in the suit array, only pointers are actually stored in the array (Fig. 7.22).  Each pointer points to the first character of its corresponding string.  Thus, even though the suit array is fixed in size, it provides access to character strings of any length.  This flexibility is one example of C’s powerful data- structuring capabilities. 11

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Question 1  What will be the output of the following code? int main(){ int a = 40; int *b = {5}; int *p = &b[0]; int y = a/*p /*divide a by *p*/; printf("y = %d\n", y); return 0; }  Answer: 40 13

Fundamentals of Strings and Characters  A string in C is an array of characters ending in the null character ('\0').  The definitions  char char color[] = color[] = "blue" "blue"; const char const char *colorPtr colorPtr = = "blue" "blue"; each initialize a variable to the string "blue" .  The first definition creates a 5-element array color containing the characters 'b' , 'l' , 'u' , 'e' and '\0' .  The second definition creates pointer variable colorPtr that points to the string "blue" somewhere in memory. 14

Character- Handling Library …  The character-handling library ( <ctype.h> ) includes several functions that perform useful tests and manipulations of character data.  Each function receives a character — represented as an int — or EOF as an argument.  EOF normally has the value – 1, and some hardware architectures do not allow negative values to be stored in char variables, so the character-handling functions manipulate characters as integers.  Figure 8.1 summarizes the functions of the character- handling library. 15

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Character- Handling Library …  Figure 8.4 demonstrates functions isspace , iscntrl , ispunct , isprint and isgraph .  Function isspace determines if a character is one of the following white-space characters: space ( ' ' ), form feed ( '\f' ), newline ( '\n' ), carriage return ( '\r' ), horizontal tab ( '\t' ) or vertical tab ( '\v' ). 21

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Question 2  What will be the output of the following code? int main(){ char arr[]="A B C D E F G H L J K M"; double *fptr; fptr=(double *)arr; fptr++; printf("%s",fptr); return 0; }  Answer: E F G H L J K M 25