Strings. A special kind of array is an array of characters ending in the null character \0 called string arrays

Transcription

1 Strings A special kind of array is an array of characters ending in the null character \0 called string arrays A string is declared as an array of characters char s[10] char p[30] When declaring a string don t forget to leave a space for the null character which is also known as the string terminator character

2 C offers four main operations on strings strcpy - copy one string into another strcat - append one string onto the right side of the other strcmp compare alphabetic order of two strings strlen return the length of a string

3 strcpy strcpy(destinationstring, sourcestring) Copies sourcestring into destinationstring For example strcpy(str, hello world ); assigns hello world to the string str

4 Example with strcpy #include <stdio.h> #include <string.h> main() char x[] = Example with strcpy ; char y[25]; printf( The string in array x is %s \n, x); strcpy(y,x); printf( The string in array y is %s \n, y);

5 strcat strcat(destinationstring, sourcestring) appends sourcestring to right hand side of destinationstring For example if str had value a big strcat(str, hello world ); appends hello world to the string a big to get a big hello world

6 Example with strcat #include <stdio.h> #include <string.h> main() char x[] = Example with strcat ; char y[]= which stands for string concatenation ; printf( The string in array x is %s \n, x); strcat(x,y); printf( The string in array x is %s \n, x);

7 strcmp strcmp(stringa, stringb) Compares stringa and stringb alphabetically Returns a negative value if stringa precedes stringb alphabetically Returns a positive value if stringb precedes stringa alphabetically Returns 0 if they are equal Note lowercase characters are greater than Uppercase

8 Example with strcmp #include <stdio.h> #include <string.h> main() char x[] = cat ; char y[]= cat ; char z[]= dog ; if (strcmp(x,y) == 0) printf( The string in array x %s is equal to that in %s \n, x,y);

9 continued if (strcmp(x,z)!= 0) printf( The string in array x %s is not equal to that in z %s \n, x,z); if (strcmp(x,z) < 0) printf( The string in array x %s precedes that in z %s \n, x,z); else printf( The string in array z %s precedes that in x %s \n, z,x); else printf( they are equal );

10 strlen strlen(str) returns length of string excluding null character strlen( tttt ) = 4 not 5 since \0 not counted

11 Example with strlen #include <stdio.h> #include <string.h> main() int i, count; char x[] = tommy tucket took a tiny ticket ; count = 0; for (i = 0; i < strlen(x);i++) if (x[i] == t ) count++; printf( The number of t s in %s is %d \n, x,count);

12 Vowels Example with strlen #include <stdio.h> #include <string.h> main() int i, count; char x[] = tommy tucket took a tiny ticket ; count = 0; for (i = 0; i < strlen(x);i++) if ((x[i] == a ) (x[i]== e ) (x[i]== I ) (x[i]== o ) (x[i]== u )) count++; printf( The number of vowels s in %s is %d \n, x,count);

13 No of Words Example with strlen #include <stdio.h> #include <string.h> main() int i, count; char x[] = tommy tucket took a tiny ticket ; count = 0; for (i = 0; i < strlen(x);i++) if ((x[i] == ) count++; printf( The number of words s in %s is %d \n, x,count+1);

14 No of Words Example with more than one space between words #include <stdio.h> #include <string.h> main() int i,j, count; char x[] = tommy tucket took a tiny ticket ; count = 0; for (i = 0; i < strlen(x);i++) if ((x[i] == ) count++; for(j=i;x[j]!= ;j++); i = j; printf( The number of words s in %s is %d \n, x,count+1);

15 Input output functions of characters and strings getchar() reads a character from the screen in a non-interactive environment getche() like getchar() except interactive putchar(int ch) outputs a character to screen gets(str) gets a string from the keyboard puts(str) outputs string to screen

16 Characters are at the heart of strings

17 Exercise 1 Output

18 #include <stdio.h> main() int i,j; for(j = 1; j <= 10; j++) for(i=1;i <= j;i++) printf( %d,i); printf( \n ); Exercise 1

19 Exercise 2 Output * * * * * * * * * *. * * * * * * * * * *

20 #include <stdio.h> main() int i,j; for(j = 1; j <= 10; j++) for(i=1;i <= j;i++) printf( * ); printf( \n ); Exercise 2

21 Exercise 3 Output *********** * * * * * * * * * * * * * * * * ***********

22 #include <stdio.h> main() int i,j; for(j = 1; j <= 10; j++) printf( * ); for(i=1;i <= 8;i++) if ((j==1) (j==10)) printf( * ); else printf( ); printf( * \n );

23 Some Useful C Character Functions Don't forget to #include <ctype.h> to get the function prototypes.

24 Functions Function int isalpha(c); Return true if c is a letter. int isupper(c); c is an upper case letter. int islower(c); c is a lower case letter. int isdigit(c); c is a digit [0-9].

25 More Functions Function Return true if int isxdigit(c); c is a hexadecimal digit [0-9A-Fa-f]. int isalnum(c); c is an alphanumeric character (c is a letter or a digit); int isspace(c); c is a SPACE, TAB, RETURN, NEWLINE, FORMFEED, or vertical tab character.

26 Even More C Functions Function int ispunct(c); int isprint(c); int iscntrl(c); Return true if c is a punctuation character (neither control nor alphanumeric). c is a printing character. c is a delete character or ordinary control character.

27 Still More C Functions Function int isascii(c); Return true if c is an ASCII character, codeless than int toupper(int c); convert character c to upper case (leave it alone if not lower) int tolower(int c); convert character c to lower case (leave it alone if not upper)

28 Program to Reverse Strings #include <stdio.h> #include <string.h> int main () int i; char a[10]; char temp; //clrscr(); // only works on windows gets(a); for (i = 0; a[i]!= '\0' ; i++); i--; for (int j = 0; j <= i/2 ; j++) temp = a[j]; a[j] = a[i - j]; a[i - j] = temp; printf("%s",a); return(0);

29 Program to count the number of Note Two different ways to declare strings One using pointers *str Two using character array char a[] #include <stdio.h> #include <string.h> vowels in a string : void main() char *str; char a[]="aeiouaeiou"; int i,j,count=0; clrscr(); printf("\nenter the string\n"); gets(str); for(i=0;str[i]!='\0';i++) for(j=0;a[j]!='\0';j++) if(a[j] == str[i] count++; break; printf("\nno. of vowels = %d",count);