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C Programming

C Programming. Character Strings Lecture 7. Topics. Strings Representation Declaration Functions Common mistakes Index of a char in a string. On the Nature of Strings. Recall: Main memory contiguous array of cells each cell has an address. 0x1FFE. 0x1FFF. 0x2000. 0x2001.

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C Programming

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  1. C Programming Character Strings Lecture 7

  2. Topics • Strings • Representation • Declaration • Functions • Common mistakes • Index of a char in a string

  3. On the Nature of Strings • Recall: Main memory • contiguous array of cells • each cell has an address 0x1FFE 0x1FFF 0x2000 0x2001 0x2002 etc.

  4. ch On the Nature of Strings (cont.) • Recall:Variable declaration • sets aside a “box” to contain a value Example: char ch; ch = ‘B’; Memory address 0x1FFE 0x1FFF 0x2000 0x2001 0x2002 etc. ‘B’

  5. On the Nature of Strings (cont.) • String declaration • sets aside an array of cells • each cell contains a char • address of first cell in the array Example: char name[5]; Specifies number of cells in the array

  6. name is 0x2000 On the Nature of Strings (cont.) • String declaration • sets aside an array of cells • each cell contains a char • address of first cell in the array Example: char name[5]; 0x2000 0x2004

  7. Character Strings Declaration 1: char name[5]; Declaration 2: #define MAXLENGTH 5 char name[MAXLENGTH]; name is 0x2000 0x2000 0x2004

  8. String Input/Output No ampersand (&)! #include <stdio.h> #define MAXLENGTH 15 int main() { char string1[MAXLENGTH]; char string2[MAXLENGTH]; scanf("%s %s", string1, string2); printf("%s %s\n", string1, string2); return 0; }

  9. More on scanf-Reading strings No ampersand (&) in scanf with strings! int main() { char user[NAMELEN]; printf("Who are you? "); scanf printf("%s\n", user); return 0; } ("%s", user);

  10. Character Strings • Terminating Character: • Marks the end of string • Special char:’\0’ • It’s really 8 zero bits Initialization: char name[5] = “Ann”; name is 0x2000 A n n \0 0x2000 0x2004

  11. Character Strings Can store at most4 letters, because of `\0’ Initialization: char name[5] = “Ann”; name is 0x2000 A n n \0 0x2000 0x2004

  12. A Char in a String The size of a character string is fixed. You can reference a character at position index: string[index] The first character has index 0

  13. A Char in a String 0x3995 0x399C name is 0x3995 J o h n \0 index 0 index 4 char name[8] = “John”; int i = 2; printf(“Char at index %d is %c.\n”, i, name[i]); output:Char at index 2 is h.

  14. A Char in a String 0x3995 0x399C name is 0x3995 J o h n \0 index 2 char name[8] = “John”; name[2] = ‘X’; printf(“Name: %s\n”, name);

  15. A Char in a String 0x3995 0x399C name is 0x3995 J o X n \0 index 2 char name[8] = “John”; name[2] = ‘X’; printf(“Name: %s\n”, name); output:Name: JoXn

  16. String Operations • #include <string.h> • Operations: • Assignment:strcpy() • Concatenation: strcat() • Comparison: strcmp(), stricmp() • Length:strlen() • See text (p38 to 39) (p108 to 109)

  17. String Operation: Assignment #include <stdio.h> #include <string.h> #define MAXLENGTH 100 int main() { char string1[MAXLENGTH]; char string2[MAXLENGTH]; strcpy(string1, “Hello World!”); strcpy(string2, string1); return 0; } string1:<garbage> string2:<garbage>

  18. String Operation: Assignment #include <stdio.h> #include <string.h> #define MAXLENGTH 100 int main() { char string1[MAXLENGTH]; char string2[MAXLENGTH]; strcpy(string1, “Hello World!”); strcpy(string2, string1); return 0; } string1:“Hello World!” string2:<garbage>

  19. String Operation: Assignment #include <stdio.h> #include <string.h> #define MAXLENGTH 100 int main() { char string1[MAXLENGTH]; char string2[MAXLENGTH]; strcpy(string1, “Hello World!”); strcpy(string2, string1); return 0; } string1:“Hello World!” string2:“Hello World!”

  20. Common Mistake: Wrong Assignment Example 1: char name1[5] = “Ann”; char name2[5] = “Dave”; name2 = name1; Error:“LValue required....”

  21. Common Mistake: Bad Assignment name2 = name1; 0x2000 A n n \0 name1 0x2000 0x2003 0x2000 D a v e \0 name2 0x3990 0x3994

  22. Common Mistake: Not enough space #define MAX 4 char name[MAX] = “Ann”; strcpy(name, “David”); name is 0x2000 A n n \0 0x2000 0x2003

  23. Common Mistake: Not enough space #define MAX 4 char name[MAX] = “Ann”; strcpy(name, “David”); name is 0x2000 D a v i d \0 0x2000 0x2003

  24. String Operation: Concatenation char string1[MAXLENGTH]; char string2[MAXLENGTH]; strcpy(string1, “Goodbye”); strcpy(string2, “, Cruel ”); strcat(string1, string2); strcat(string1, string2); strcat(string1, “World!”); string1:“Goodbye” string2:“, Cruel “

  25. String Operation: Concatenation char string1[MAXLENGTH]; char string2[MAXLENGTH]; strcpy(string1, “Goodbye”); strcpy(string2, “, Cruel ”); strcat(string1, string2); strcat(string1, string2); strcat(string1, “World!”); string1:“Goodbye, Cruel ” string2:“, Cruel “

  26. String Operation: Concatenation char string1[MAXLENGTH]; char string2[MAXLENGTH]; strcpy(string1, “Goodbye”); strcpy(string2, “, Cruel ”); strcat(string1, string2); strcat(string1, string2); strcat(string1, “World!”); string1:“Goodbye, Cruel , Cruel ” string2:“, Cruel “

  27. String Operation: Concatenation char string1[MAXLENGTH]; char string2[MAXLENGTH]; strcpy(string1, “Goodbye”); strcpy(string2, “, Cruel ”); strcat(string1, string2); strcat(string1, string2); strcat(string1, “World!”); string1:“Goodbye, Cruel , Cruel World!” string2:“, Cruel “

  28. Common Mistake: Not enough space char name[5]; strcpy(name, “Ann”); strcat(name, “ Smith”); name is 0x2000 A n n \0 0x2000 0x2004

  29. Common Mistake: Not enough space #define MAX 5 char name[MAX]; strcpy(name, “Ann”); strcat(name, “ Smith”); name is 0x2000 A n n S m i t h \0 0x2000 0x2004

  30. String Operation: Comparison strcpy(string1, “Apple”); strcpy(string2, “Wax”); if (strcmp(string1, string2) < 0) { printf(“%s %s\n”, string1, string2); } else { printf(“%s %s\n”, string2, string1); } output:Apple Wax

  31. String Operation: Comparison strcpy(string1, “Apple”); strcpy(string2, “Wax”); if (strcmp(string1, string2) < 0) { printf(“%s %s\n”, string1, string2); } else { printf(“%s %s\n”, string2, string1); } Returns: negative if string1 < string2 zero if string1 == string2 positive if string1 > string2

  32. Common Mistake: Wrong Comparison strcpy(string1, “Apple”); strcpy(string2, “Wax”); if (string1 < string2) { printf(“%s %s\n”, string1, string2); } else { printf(“%s %s\n”, string2, string1); }

  33. Number of char’s before the `\0’. String Operation: Length #define MAX 100 char string1[MAX]; int len strcpy(string1, “Apple”); len=strlen(string1); printf(“%d\n”, len); output:5

  34. name is 0x3990 D a v i d \0 0x3990 0x3994 Common Mistake: Not enough space #define MAX 5 char name[MAX]; strcpy(name, “David”); Don’t forget the ‘\0’.

  35. Summary • A string is a contiguous array of chars that ends with the null character ‘\0’ • The string identifier is the address of the first char in the string • Individual chars are accessed using the str[index] notation • There are C library functions for copying, concatenating and comparing strings.

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