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Strings

Strings. A special kind of array is an array of characters ending in the null character called string arrays A string is declared as an array of characters char s[10] char p[30]

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Strings

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  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() { inti,j, count; char x[] = “tommytucket 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(intch) outputs a character to screen • gets(str) gets a string from the keyboard • puts(str) outputs string to screen

  16. Exercise 1 Output 1 1 2 1 2 3 1 2 3 4 …………. 1 2 3 4 5 6 7 8 9 10

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

  18. Exercise 2 Output * * * * * * * * * * ……………. * * * * * * * * * *

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

  20. Exercise 3 • Output *********** * * * * * * * * * * * * * * * * ***********

  21. #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 “); } }

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

  23. Functions • Function Return true if • int isalpha(c); 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].

  24. 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.

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

  26. Still More C Functions • Function Return true if • int isascii(c); c is an ASCII character, code less than 0200. • 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)

  27. Program to Reverse Strings #include <stdio.h> #include <string.h> int main () { inti; 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); }

  28. Program to count the number of vowels in a string : Note Two different ways to declare strings One using pointers *str Two using character array char a[] #include <stdio.h> #include <string.h> void main() { char *str; char a[]="aeiouAEIOU"; inti,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); } }

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