Chapter 8 Character Arrays and Strings PROGRAMMING IN ANSI C

c[0]=72; c[1]=101; c[2]=c[3]=108; c[4]=111; 2/18/2019 Character Arrays In a character array, each element stores one character. e.g. char c[5]; c[0]='H'; c[1]='e'; c[2]=c[3]='l'; c[4]='o'; c[0] H c[1] e c[2] l c[3] c[4] o c[0]=72; c[1]=101; c[2]=c[3]=108; c[4]=111;

Character Arrays - Initialization 2/18/2019 Character Arrays - Initialization Like other type one-dimensional arrays, the character array can be initialized in the same way. e.g. char c[5] = { 'H', 'e', 'l', 'l', 'o' }; If the number of initializers is less than the declared size, the remaining elements are initialized to null character ('\0'). e.g. char c[6] = { 'H', 'e', 'l', 'l', 'o' }; c[0] H c[1] e c[2] l c[3] c[4] o c[5] \0 c[0] H c[1] e c[2] l c[3] c[4] o

Character Arrays - Initialization 2/18/2019 Character Arrays - Initialization Like other type one-dimensional arrays, the character array can be initialized in the same way. e.g. char c[5] = { 'H', 'e', 'l', 'l', 'o' }; If the number of initializers is more than the declared size, the complier will produce an error. e.g. char c[4] = { 'H', 'e', 'l', 'l', 'o' }; c[0] H c[1] e c[2] l c[3] c[4] o Error … : Too many initializers in function ...

Character Arrays - Initialization 2/18/2019 Character Arrays - Initialization Like other type one-dimensional arrays, the character array can be initialized in the same way. e.g. char c[5] = { 'H', 'e', 'l', 'l', 'o' }; If the number of initializers is equal to the declared size, the size may be omitted. e.g. char c[ ] = { 'H', 'e', 'l', 'l', 'o' }; c[0] H c[1] e c[2] l c[3] c[4] o

2/18/2019 Character Arrays The character array can be used as other type one-dimensional arrays. I am happy main() { char c[10] = { 'I', '', 'a', 'm', '', 'h', 'a', 'p', 'p', 'y' }; int i; for ( i = 0; i < 10; i++ ) printf ( "%c", c[i] ); }

Strings A string is a character array. 2/18/2019 Strings A string is a character array. char c[10] = { 'I', '', 'a', 'm', '', 'h', 'a', 'p', 'p', 'y' }; The actual length of the string is not always equal to the size of the character array. In fact, we often concern the actual length of a string rather than the size of a character array. char c[100] = { 'I', '', 'a', 'm', '', 'h', 'a', 'p', 'p', 'y' }; The size of the character array is 100, but the actual length of the string is only 10.

2/18/2019 Strings The array size is often much larger than the size of the string stored in the array. In order to represent the end of the string, the null character '\0' is used as the "end-of-string" marker. char c[5] = { 'B', 'o ', 'y' }; c[0] B c[1] o c[2] y c[3] \0 c[4] c[3] is the "end-of-string" marker '\0', so the elements before it compose the string, and the length of the string is 3.

2/18/2019 Strings Pay attention to the distinction of the null character '\0', and the blank space character '', and the figure character '0'. The ASCII value of '\0' is 0. It can't be displayed and acts as the "end-of-string" marker. The ASCII value of '' is 32. It can be outputted as a blank and occupy one place. The ASCII value of '0' is 48. It can be outputted as a figure.

2/18/2019 Strings When a string constant is stored in memory, it also uses the null character '\0' as the "end-of-string" marker. For example: When the string "Hello" is stored in memory, it requires 6 bytes storage, and the last byte is used to store the null character '\0'.

Strings - Initialization 2/18/2019 Strings - Initialization Using characters. char c[5] = { 'G', 'o ', 'o', 'd' }; Using string. char c[5] = { "Good" }; char c[5] = "Good"; char c[ ] = "Good"; c[0] G c[1] o c[2] c[3] d c[4] \0 Notice: The array c consists of 5 elements but not 4 elements! This declaration is equivalent to: char c[5] = "Good"; It differs with char c[4] = "Good";

Strings - Initialization 2/18/2019 Strings - Initialization The initialization of table of strings. char fruit[ ][7] = { "Apple", "Orange", "Grape", "Pear", "Peach"}; \0 h c a e P fruit[4] r fruit[3] p G fruit[2] g n O fruit[1] l A fruit[0]

Input and Output – %c abcde abcde _ abcdefg abcdef_ %c main() 2/18/2019 Input and Output – %c abcde abcde _ abcdefg abcdef_ %c main() { char str[6]; int i; for ( i = 0; i < 6; i++ ) scanf ( "%c", &str[i] ); printf ( "%c", str[i] ); }

Input and Output – %s abc abc_ str[0] a str[1] b str[2] c str[3] \0 2/18/2019 Input and Output – %s abc abc_ str[0] a str[1] b str[2] c str[3] \0 str[4] ? str[0] ? str[1] str[2] str[3] str[4] %s main() { char str[5]; scanf ( "%s", str ); printf ( "%s", str ); } str is the address of the string (character array), don't use &str. The number of the input characters should be less than 5. "blank space" or "tab" or "newline" marks the end of the input string. The "end-of string" marker '\0' is stored automatically. The string is outputted from the address str (the address of the string), and stopped when the element is the "end-of string" marker '\0'.

Input and Output – %s # a -> H e l o \0 = s " @ # a -> H e l o = 2/18/2019 Input and Output – %s # a -> H e l o \0 = s " @ # a -> H e l o = s \0 " @ # ê ¬ 7 $ f = s \0 " @ %s Hello#=s main() { char a[ ] = { 'H', 'e', 'l', 'l', 'o' }; printf ( "%s", a ); } Hello main() { char a[ ] = "Hello"; printf ( "%s", a ); }

Input and Output – %s # a -> H e l \0 = s " @ # a -> H e l o = s 2/18/2019 Input and Output – %s # a -> H e l \0 = s " @ # a -> H e l o = s \0 " @ # ê ¬ 7 $ f = s \0 " @ %s Hell main() { char a[5] = { 'H', 'e', 'l', 'l' }; printf ( "%s", a ); } Error … : Too many initializers in function ... Hello#=s main() { char a[5] = "Hello"; printf ( "%s", a ); } main() { char a[4] = "Hello"; printf ( "%s", a ); }

Input and Output – %s # a -> H e l \0 o ! " @ # ê ¬ 7 $ f = s \0 " 2/18/2019 Input and Output – %s # a -> H e l \0 o ! " @ # ê ¬ 7 $ f = s \0 " @ %s Hell main() { char a[ ] = {'H', 'e', 'l', 'l', '\0', 'o', '!', '\0'}; printf ( "%s", a ); } The output begins from the address "a" and ends when it encounters the first null character.

2/18/2019 The length of the input string must be less than the length of the array! Input and Output – %s address: a: ffd2, n: ffd6 a: ê¬7$, n: 1 Please input a string: abcd a: abcd, n: 0 address: a: ffd2, n: ffd6 a: ê¬7$, n: 1 Please input a string: abcde a: abcde, n: 101 address: a: ffd2, n: ffd6 a: ê¬7$, n: 1 Please input a string: abc a: abc, n: 1 # a -> 'ê' '¬' '7' '$' n -> 1 '*' 's' ']' '@' # a -> 'a' 'b' 'c' 'd' n -> 'e' \0 '*' 's' ']' '@' # a -> 'a' 'b' 'c' \0 n -> 1 '*' 's' ']' '@' # a -> 'a' 'b' 'c' 'd' n -> \0 '*' 's' ']' '@' %s main() { char a[4]; int n = 1; printf ( "address: a: %x, n: %x\n", a, &n ); printf ( "a: %s, n: %d\n", a, n ); printf ( "Please input a string:\n" ); scanf ( "%s", a ); printf ( "a: %s, n: %d", a, n ); }

"blank space" or "tab" or "newline" marks the end of the input string. 2/18/2019 Input and Output – %s How are you? a=How b=are c=you? %s main() { char a[15], b[5], c[5]; scanf ( "%s%s%s", a, b, c ); printf ( "a=%s\nb=%s\nc=%s\n", a, b, c ); } "blank space" or "tab" or "newline" marks the end of the input string. a b c \0 w o H e r a ? u y

   Input and Output – %s char s[100], c; int k; 2/18/2019 Input and Output – %s char s[100], c; int k; Question: We want to input a string "This is a string.". Can the following statements read in this string correctly? (A) scanf ( "%17s", s ); (B) for ( k = 0; k < 17; k++ ) s[k] = getchar(); (C) k = 0; while ( ( c = getchar() ) != '\n' ) s [k++] = c; s [k] = 0;   

Input and Output – puts( ) 2/18/2019 Input and Output – puts( ) How do you do? I'm Ok. Thank you. _ How do you do? _ puts( ) Form: puts (str) After it outputs the string, it moves the cursor to the next line automatically. main() { char c[ ] = "How do you do?"; puts ( c ); puts ( "I'm OK. Thank you." ); }

Input and Output – gets( ) 2/18/2019 Input and Output – gets( ) gets( ) Form: gets (str) It is used to read a line of text. Only the "newline" character marks the end of the input string. The "blank space" and "tab" will be read in as a character in the string. How are you? _ main() { char c[50]; gets ( c ); puts ( c ); }

String-Handling Functions – strcat( ) 2/18/2019 String-Handling Functions – strcat( ) strcat (str1, str2) Function: Concatenates 2 strings (str2 is appended to str1). Return value: The address of str1. str1 \0  w o H \0 e r a  w o H \0 e r a str2 How are are _ How are _ #include <string.h> main() { char str1[10]="How "; char str2[5]="are"; puts ( strcat ( str1,str2 ) ); puts ( str2 ); } #include <string.h> main() { char str1[10]="How "; char str2[5]="are"; strcat ( str1,str2 ); puts ( str1 ); puts ( str2 ); }

String-Handling Functions – strcat( ) 2/18/2019 String-Handling Functions – strcat( ) strcat (str1, str2) Function: Concatenates 2 strings (str2 is appended to str1). Return value: The address of str1. We can't use such statement to join 2 strings together: str1 = str1 + str2; str1 and str2 both are address values; str1 is an address constant, and it can't be assigned by any value again.

String-Handling Functions – strcpy( ) 2/18/2019 String-Handling Functions – strcpy( ) strcpy (str1, str2) Function: Copies one string (str2) over another (str1). Return value: The address of str1.

String-Handling Functions – strcpy( ) 2/18/2019 String-Handling Functions – strcpy( ) #include <string.h> main() { char tc[10]; char b[ ] = " "; char c[ ]= "C"; char t[ ] = "Turbo"; strcpy ( tc, t ); strcat ( tc, b ); strcat ( tc, c ); printf("%s\n", tc); } tc ! 9 y 8 \0 7 C 6  5 o 4 b 3 r 2 u 1 T ! 9 y 8 G 7 : 6 & 5 ( 4 @ 3 2 $ 1 ^ ! 9 y 8 G 7 \0 6  5 o 4 b 3 r 2 u 1 T ! 9 y 8 G 7 : 6 \0 5 o 4 b 3 r 2 u 1 T Turbo C \0 o b r u T C  c t

String-Handling Functions – strcpy( ) 2/18/2019 String-Handling Functions – strcpy( ) strcpy (str1, str2) Function: Copies one string (str2) over another (str1). Return value: The address of str1. We can't use an assignment statement to assign any string to a character array (expect the initialization). char str1[10] = "How ", str2[10]; str2 = "How "; str1 = str2; strcpy ( str1, str2 );  

String-Handling Functions – strcmp( ) 2/18/2019 String-Handling Functions – strcmp( ) strcmp (str1, str2) Function: Compares two strings. It compares the characters of st1 and str2 one by one. And it will stop when it finds the first different character or it encounters one null character. Return value: When the function stops the comparison, the difference of the ASCII value between the current character of str1 and that of str2. strcmp ( "A", "B" ) strcmp ( "a", "A" ) strcmp ( "ABC", "AB" ) strcmp ( "computer", "compare" ) strcmp ( "36", "3654" ) => 'A' – 'B' => -1 => 'a' – 'A' => 32 => 'C' – '\0' = 67 => 'u' – 'a' = 20 => '\0' – '5' = -53

String-Handling Functions – strcmp( ) 2/18/2019 String-Handling Functions – strcmp( ) strcmp (str1, str2) We can't use "==" operator to compare two strings. while ( st1 == str2 ) ... change to: while ( strcmp(str1, str2) == 0 ) or while ( ! strcmp(str1, str2) )

String-Handling Functions – strlen( ) 2/18/2019 String-Handling Functions – strlen( ) strlen (str) Function: Return the length of the string (the number of the characters of str except the null character). For these following declarations, what is the value of the function strlen(s)? (1) char s[10] = {'A', '\0', 'B', 'C', '\0', 'D'}; (2) char s[ ]="\t\b\\\0will\n"; (3) char s[ ]="\x69\082\n"; 1 ("A") 3 ("\t\b\\") 1 ("i")

2/18/2019 String - Program 1 Write a program to calculate the length of a string. Don't use the function strlen(). Step 1: Declare a character array s[100]; Step 2: Read in a string. Step 3: Calculate the number of the characters before the first null character in s. It is the length of s. Step 4: Output the value of the number.

String - Program 1 Please input the string: How are you? 2/18/2019 String - Program 1 Please input the string: How are you? The length of string is 3. Please input the string: Hello The length of string is 5. main() { char s[100]; int i = 0, slen = 0; printf ( "Pleas input the string:\n" ); scanf ( "%s", s ); while ( s[i] != '\0' ) { slen ++; i++; } printf ( "The length of string is: %d\n", slen ); while ( s[i] != 0 ) while ( s[i] )

2/18/2019 String - Program 2 \0 z y x b a d c \0 z y x d c b a Write a program to concatenate 2 strings. Don't use the function strcat(). Step 1: Declare two character arrays a[100], b[50]; Step 2: Read two strings into arrays a and b. Step 3: Begin with the null character of the array a to copy all the characters before the null character of array b into array a. Step 4: Output the arrays a and b.

String - Program 2 main() { char a[100], b[50]; int i = 0, j = 0; 2/18/2019 String - Program 2 main() { char a[100], b[50]; int i = 0, j = 0; printf ( "Pleas input 2 strings:\n" ); scanf ( "%s%s", a, b ); while ( a[i] != 0 ) i++; while ( b[j] != 0 ) { a[i] = b[j]; i++; j++; } a[i] = 0; printf ( "a: %s\nb: %s\n", a, b ); Please input 2 strings: Good boy! a: Goodboy! b: boy!

2/18/2019 String - Program 3 Write a program to reverse the characters of a string. Step 1: Declare a character arrays a[50]; Step 2: Read a string into a. Step 3: Get the subscript of the null character of the array a, and assign it to variable i. Step 4: for ( j = 0; j < i; j++, i-- ) exchange a[i] and a[j].

String - Program 3 main() { char a[30], ch; int i = 0, j = 0; 2/18/2019 String - Program 3 main() { char a[30], ch; int i = 0, j = 0; printf ( "Pleas input the string:\n" ); scanf ( "%s", a ); while ( a[i] != 0 ) i ++; i--; for ( j = 0; j < i; j++, i-- ) { ch = a[j]; a[j] = a[i]; a[i] = ch; } printf ( "%s\n", a ); Please input the string: abcd dcba j <= i / 2 a \0 d c b \0 a b c d \0 a c b d i j j i j i i

Homework Review Questions P243 2/18/2019 Homework Review Questions P243 8.1, 8.2 [except (h)], 8.6~8.10 (Write down in your exercise book) Programming Exercises