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Characters

Programming. Characters. Data Type: char. Constant declaration const char star = '*'; Variable declaration char resp; Variable assignment resp = 'c'; Input/Output char a, b, c, d; cin >> a >> b >> c >> d; // user types: 1X3Y // a <- '1', b<-'X', c<-'3', d<-'Y'

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Characters

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  1. Programming Characters

  2. Data Type: char • Constant declaration const char star = '*'; • Variable declaration char resp; • Variable assignment resp = 'c'; • Input/Output char a, b, c, d; cin >> a >> b >> c >> d; // user types: 1X3Y // a <- '1', b<-'X', c<-'3', d<-'Y' cout <<a<< ' ' <<b<< ' ' <<c<< ' ' <<d<< endl; // output: 1 X 3 Y

  3. The ASCII Character Set • 7-bit encoding for 128 possible characters • Some of the 32 non-printing control characters • 0 NUL character (end of string character) • 7 Bell character (makes beep) • 8 Backspace character (\b) • 9 Tab character (\t) • 10 Newline character (\n) • space (32) is the first printable ACSII character • '0' - '9' have code values 48 through 57 • 'A' - 'Z' have code values 65 through 90 • 'a' - 'z' have code values 97 through 122 • See Appendix A.1 in book for full ASCII list

  4. The ASCII Character Set • www.asciitable.com Use 1: perform arithmetics Use 2: perform comparison

  5. Characters: Example 3 // program to output a random character #include <iostream> #include <cstdlib> #include <ctime> using namespace std; void main(){ char c; int r; srand(time(0)); r = rand()%26; c = 'a' + r; // addition with characters!! cout << "random character: " << c << endl; }

  6. Relational char Operators • '0' - '9' have code values 48 through 57 '0' < '1' < ... < '9' • 'A' - 'Z' have code values 65 through 90 'A' < 'B' < ... < 'Z' • 'a' - 'z' have code values 97 through 122 'a' < 'b' < ... < 'z' • (Upper case is always < lower case)

  7. Character Functions in <cctype> • isupper(c) returns nonzero if c is an uppercase letter • islower(c) returns nonzero if c is a lowercase letter • isalpha(c) returns nonzero if either islower(c) or isupper(c) returns nonzero • isdigit(c) returns nonzero if c is a digit character • isalnum(c) returns nonzero if either isalpha(c) or isdigit(c) returns nonzero • isspace(c) returns nonzero if c is a space, newline, or tab • tolower(c) if c is uppercase it returns lowercase; otherwise it returns c • toupper(c) if c is lowercase it returns uppercase; otherwise it returns c

  8. Characters: Example 1 // islower.cpp #include <iostream> using namespace std; int islower(char c){ if(c>='a' && c <='z') return 1; else return 0; } void main(){ char c; cout << "Enter a character: "; cin >> c; if(islower(c)) cout << c << " is a lower case letter" << endl; else cout << c << " is not a lower case letter\n"; }

  9. Characters: Example 2 // program to beep at user #include <iostream> using namespace std; void main(){ cout << '\7'; // print ASCII code 7 cout << '7'; // print character '7' }

  10. White Space • cin >> c skips any white space (spaces, tabs, newlines) • Example: char c = ' '; while(c != '\n') cin >> c; cout << c; } • Input: a b c d • Output: abcd

  11. Difference between cin.get(ch) and >> • How to keep white spaces? • Use cin.get(ch): char ch = ' '; while(ch != '\n') cin.get(ch); // ch is passed by reference // ch is set to the input value cout.put(ch); // ch is passed by value // just print it out; // same as: cout << ch; } • Input: a b c d • Output: a b c d • cin.get(ch) reads white space just like other characters!!

  12. cin.get(c) • cin.get (char&) read a single character • cout.put (char) write a single character • Let's say the user inputs a word, 'hello'. cin.get(c) will return the letter 'h'. The rest of the word is not lost, but stays in the stream. • If we perform another cin.get operation, we will get the next letter, 'e'. • cout.put(c) simply outputs one letter at a time (same as cout << c).

  13. cin.get(c): Example 1 // Program to count the number of input blanks // (Program outputs characters without blanks) #include <iostream> using namespace std; void main() { char next; int count = 0; do{ cin.get(next); if(next == ' ') count++; else cout.put(next); }while(next != '\n'); cout << "Number of blanks = " << count << endl; }

  14. cin.get(c): Example 1 Input: a Output: a Number of blanks = 0 Input: ab cd Output: abcd Number of blanks = 1 Input: 1 2 3 4 5 6 7 8 9 Output: 123456789 Number of blanks = 8

  15. cin.get(c): Example 2 /* Reads a string of characters and converts the digits in the string to int type */ #include <iostream> #include <cctype> using namespace std; int read_int(); void main() { int number; cout << "Enter a line of digits followed by enter: "; number = read_int(); cout << "The numerical value of the digits" << " in the line is: \n" << number << endl; }

  16. cin.get(c): Example 2 int read_int(){ const char nwln = '\n'; char next; int digit; int value = 0; do{ cin.get(next); if(isdigit(next)){ digit = int(next) - int('0'); value = 10*value + digit; } }while(next != nwln); return value; }

  17. cin.get(c): Example 2 Enter a line of digits followed by enter: 1a234 The numerical value of the digits in the line is: 1234 Enter a line of digits followed by enter: 1234567890 The numerical value of the digits in the line is: 1234567890 Enter a line of digits followed by enter: 12345678900 The numerical value of the digits in the line is: -539222988 (overflows at about 2.147 billion with 32-bit integers)

  18. Programming Strings

  19. Strings • Strings are a special data type used to store a sequence of characters • Include the <string> library to use strings • Compare strings with the <, ==, and != operations • Concatenate strings with the + operation • Use s.substr(position, size) to get a substring from a string s starting from position, and of length size • Use s.find(subs) to find where a substring subs begins in string s

  20. Strings: Example 1 #include <iostream> #include <string> // string library using namespace std; int main(){ string name; cout << "Enter name (without spaces): "; cin >> name; cout << "Name: " << name << endl; } • example input/output: Enter name (without spaces): ChanTaiMan Name: ChanTaiMan

  21. Strings: Example 2 #include <iostream> #include <string> // string library using namespace std; int main(){ string s = "Top "; string t = "ten "; string w; string x = "Top 10 Uses for Strings"; w = s + t; cout << "s: " << s << endl; cout << "t: " << t << endl; cout << "w: " << w << endl; cout << "w[5]: " << w[5] << endl;

  22. Strings: Example 2 if(s < t) cout << "s alphabetically less than t" << endl; else cout << "t alphabetically less than s" << endl; if(s+t == w) cout << "s+t = w" << endl; else cout << "s+t != w" << endl; cout << "substring where: " << x.find("Uses") << endl; cout << "substring at position 12 with 7 characters: " << x.substr(12, 7) << endl; return 0; }

  23. Strings: Example 2 • Example output: s: Top t: ten w: Top ten w[5]: e s alphabetically less than t s+t = w substring where: 7 substring at position 12 with 7 characters: for Str

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