1. CS 1400
27 Nov 2006
C-strings

2. Character Testing… #include <cctype>
Functions: (returning true or false)
bool isalpha (char c);
bool isalnum (char c);
bool isdigit (char c);
bool islower (char c);
bool isupper (char c);
bool isprint (char c);
bool ispunct (char c);
bool isspace (char c);

3. Character Conversion…
#include <cctype>
Functions: (returning a char result)
char toupper (char c);
char tolower (char c);
Example:
char c;
cin >> c;
cout << toupper(c);

4. C-strings with char arrays…
An older, traditional way of representing strings
declaration: char name[30], line[30];
null char termination
cin >> name;
cout << name;
cout << “hello world!”;
no direct assignment! line = name;
no direct comparison! if (name < line)…

5. C-strings with char arrays…
Functions:
int strlen (char *str);
Returns the length of the C-string in array str.
Example:
char word[30];
cout << “word length: “ << strlen(word);

6. C-strings with char arrays…
Functions:
void strcat (char *str1, char *str2);
Concatenates str2 onto the end of str1.
Example:
char word[30], line[80];
cin >> line;
cin >> word;
strcat (line, word);
cout << “complete line: “ << line;

7. C-strings with char arrays…
Functions:
void strcpy (char *dest, char *source);
void strncpy (char *dest, char *source, int length);
Copies source into dest array (including null char).
Example:
char word[30], line[80];
cin >> word;
strcpy (line, word);
cout << “copied word: “ << line;
strncpy (line, word, 5);
cout << “first 5 chars of word: “” << line;

8. C-strings with char arrays…
Functions:
int strcmp (char *str1, char *str2);
Compares strings in str1 and str2, returning <0, 0, or >0
Example:
char word[30], line[80];
cin >> line;
cin >> word;
if (strcmp(line, word) < 0)
cout << “line is alphabetically less than word”;
if (strcmp(line, word) == 0)
cout << “line is alphabetically equal to word”;

9. C-strings with char arrays…
Functions:
char *strstr (char *str, char *target);
Returns pointer to first occurrence of target in str (or NULL)
Example:
char *a = “hello my friend”, *b = “my”;
char *c = strstr(a, b);
if (c != NULL)
cout << “string b is found within string a”;
*c = toupper(*c);
cout << “capitalized target: “ << a;

10. C-string conversions #include <cstdlib> Functions:
int atoi (char *str);
Convert numeric digits in str into an integer
float atof (char *str);
Convert numeric digits in str into a float
Example:
char word[] = {“1234”};
int x;
cin >> x;
if (x < atoi(word))
cout << “x is less than word”;

11. C-string conversions Functions:
void sprintf_s (char *str, char *format, {args} );
Convert number arguments in str according to format
Format placeholders:
%d place the next argument here as an int
%f place next argument here as a float
%8d place next argument in next 8 spaces as an
int
%10.2f place next argument in next 10 spaces,
rounded to 2 decimal places as a float

12. C-string conversions Example: float x = 3.14159; int y = 123;
char line[80];
sprintf_s (line, “x is: %f y is: %d”, x, y);
cout << line;
sprintf_s (line, “x is: %8.2f y is: %4d”, x, y);

13. C-strings vs. C++ string
char word[30];
cin >> word;
cout << “word length: “ << strlen(word);
string word;
cout << “word length: “ << word.length();

14. C-strings vs. C++ string
char word[30], line[80];
cin >> line;
cin >> word;
strcat (line, word);
cout << “complete line: “ << line;
string word, line;
line += word;
cout << “completed line: << line;

15. C-strings vs. C++ string
char word[30], line[80];
cin >> word;
strcpy (line, word);
cout << “copied word: “ << line;
string word, line;
line = word;
cout << “copied word: << line;

16. C-strings vs. C++ string
char word[30], line[80];
cin >> line >> word;
if (strcmp(line, word) < 0)
cout << “line is alphabetically less than word”;
string word, line;
if (line < word)

17. C-strings vs. C++ string
char *a = “hello my friend”, *b = “my”;
char *c = strstr(a, b);
if (c != NULL)
cout << “string b is found within string a”;
string a = “hello my friend”, b = “my”;
int n = a.find(b);
if (n >= 0)

18. C-strings vs. C++ string
char *a = “hello my friend”, *b = “my”;
char *c = strstr(a, b);
*c = toupper(*c);
string a = “hello my friend”, b = “my”;
int n = a.find(b);
a[n] = toupper(a[n]);

19. C-strings vs. C++ string
C++ string has over 30 additional manipulation functions!
Why would anyone want to use C-strings?
Using C++ string variables significantly increases the size of your program (and perhaps decreases efficiency).
Historically, C-strings were used long before string was available.