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C Strings

C Strings. Types of Strings. String Literals: “Hello World” “xyz 123 *&^#$!” C-style strings: char s[20]; C++ class string; string s;. literalString.cpp. ... int main() { char s[] = "Hello World"; cout << s << endl; for (int i = 0; i < 11; i++)

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C Strings

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  1. C Strings The Ohio State University

  2. Types of Strings • String Literals: “Hello World” “xyz 123 *&^#$!” • C-style strings: char s[20]; • C++ class string; string s; The Ohio State University

  3. literalString.cpp ... int main() { char s[] = "Hello World"; cout << s << endl; for (int i = 0; i < 11; i++) { cout << s[i] << ","; } cout << endl; ... The Ohio State University

  4. literalString.cpp ... char s[] = "Hello World"; cout << s << endl; for (int i = 0; i < 11; i++) { cout << s[i] << ","; } cout << endl; ... > literalString.exe Hello World H,e,l,l,o, ,W,o,r,l,d, The Ohio State University

  5. Literal String • To create a variable containing a literal string: char s[] = “Hello World”; • char s[] means an array of characters; • This variable cannot be changed, i.e., the following will generate a syntax error: char s[] = “Hello World”; s = “Goodbye World”; // Syntax Error The Ohio State University

  6. ascii.cpp ... int main() { char s[] = "Hello World"; cout << s << endl; for (int i = 0; i < 11; i++) { cout << setw(4) << s[i] << ","; } cout << endl; for (int i = 0; i < 11; i++) { cout << setw(4) << int(s[i]) << ","; } cout << endl; return 0; } The Ohio State University

  7. ... char s[] = "Hello World"; cout << s << endl; for (int i = 0; i < 11; i++) { cout << setw(4) << s[i] << ","; } cout << endl; for (int i = 0; i < 11; i++) { cout << setw(4) << int(s[i]) << ","; } cout << endl; ... > ascii.exe Hello World H, e, l, l, o, , W, o, r, l, d, 72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, > The Ohio State University

  8. null Character • Literal strings end in a null character: ‘\0’. (Character ‘\0’ has ASCII code 0.) char s[] = “Hello World”; • s[0] equals ‘H’; • s[1] equals ‘e’; . . . • s[8] equals ‘r’; • s[9] equals ‘l’; • s[10] equals ‘d’; • s[11] equals ‘\0’; The Ohio State University

  9. literalString2.cpp ... int i; char s[] = "Hello World"; cout << s << endl; i = 0; while(s[i] != '\0') { cout << s[i] << ","; i++; } cout << endl; cout << "s[" << i << "] = " << int(s[i]) << endl; ... The Ohio State University

  10. literalString2.cpp cout << s << endl; i = 0; while(s[i] != '\0') { cout << s[i] << ","; i++; } cout << endl; cout << "s[" << i << "] = " << int(s[i]) << endl; > literalString2.exe Hello World H,e,l,l,o, ,W,o,r,l,d, s[11] = 0 The Ohio State University

  11. ascii2.cpp ... i = 0; while(s[i] != '\0') { cout << setw(4) << s[i] << ","; i++; } cout << endl; i = 0; while(s[i] != '\0') { cout << setw(4) << int(s[i]) << ","; i++; } cout << setw(4) << int(s[i]); cout << endl; ... The Ohio State University

  12. ... i = 0; while(s[i] != '\0') { cout << setw(4) << int(s[i]) << ","; i++; } cout << setw(4) << int(s[i]); cout << endl; ... > ascii2.exe Hello World H, e, l, l, o, , W, o, r, l, d, 72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 0 > The Ohio State University

  13. C-style strings • A C-style string is stored in an array of char; • C-style strings should always end in ‘\0’; const int MAX_LENGTH(20); char s[MAX_LENGTH] = { 'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '\0'}; cout << "String = " << s << endl; The Ohio State University

  14. cString.cpp const int MAX_LENGTH(20); // C-style strings should always end in '\0' char s[MAX_LENGTH] = { 'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '\0'}; cout << "String = " << s << endl; s[1] = 'o'; s[2] = 'w'; s[3] = 'd'; s[4] = 'y'; cout << "String = " << s << endl; s[5] = '\0'; cout << "String = " << s << endl; The Ohio State University

  15. cString.cpp const int MAX_LENGTH(20); // C-style strings should always end in '\0' char s[MAX_LENGTH] = { 'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '\0'}; cout << "String = " << s << endl; s[1] = 'o'; s[2] = 'w'; s[3] = 'd'; s[4] = 'y'; cout << "String = " << s << endl; s[5] = '\0'; cout << "String = " << s << endl; > cString.exe String = Hello World String = Howdy World String = Howdy The Ohio State University

  16. Literal String • A literal string variable cannot be changed, i.e., the following will generate a syntax error: char s[] = “Hello World”; s = “Goodbye World”; // Syntax Error • However, individual characters within the string can be changed: s[1] = 'o'; s[2] = 'w'; • A literal string should ALWAYS contain ‘\0’. The Ohio State University

  17. Capitalize Change all characters in a string to capitals. Input: Hello World Output: HELLO WORLD The Ohio State University

  18. ASCII Code The Ohio State University

  19. capitalize.cpp ... char s[] = "Hello World"; int ascii_code(0); int i(0); cout << s << endl; i = 0; while(s[i] != '\0') { ascii_code = int(s[i]); if (97 <= ascii_code && ascii_code <= 122) { ascii_code = ascii_code-32; } cout << char(ascii_code); i++; } cout << endl; ... The Ohio State University

  20. … i = 0; while(s[i] != '\0') { ascii_code = int(s[i]); if (97 <= ascii_code && ascii_code <= 122) { ascii_code = ascii_code-32; } cout << char(ascii_code); i++; } … > capitalize.exe Hello World HELLO WORLD The Ohio State University

  21. passLiteral.cpp ... int main() { int x1, y1; int x2, y2; read_point("Enter first point: ", x1, y1); read_point("Enter second point: ", x2, y2); write_point("First point: ", x1, y1); write_point("Second point: ", x2, y2); return 0; } ... The Ohio State University

  22. passLiteral.cpp ... void read_point(const char prompt[], int & x, int & y); void write_point(const char label[], int x, int y); int main() { int x1, y1; int x2, y2; read_point("Enter first point: ", x1, y1); read_point("Enter second point: ", x2, y2); write_point("First point: ", x1, y1); write_point("Second point: ", x2, y2); return 0; } ... The Ohio State University

  23. Functions read_point() and write_point() void read_point(const char prompt[], int & x, int & y) { cout << prompt; cin >> x; cin >> y; } void write_point(const char label[], int x, int y) { cout << label; cout << "(" << x << "," << y << ")" << endl; } The Ohio State University

  24. … read_point("Enter first point: ", x1, y1); read_point("Enter second point: ", x2, y2); … void read_point(const char prompt[], int & x, int & y) { cout << prompt; cin >> x; cin >> y; } > passLiteral.exe Enter first point: 10 20 Enter second point: 3 5 First point: (10,20) Second point: (3,5) The Ohio State University

  25. … write_point("First point: ", x1, y1); write_point("Second point: ", x2, y2); … void write_point(const char label[], int x, int y) { cout << label; cout << "(" << x << "," << y << ")" << endl; } > passLiteral.exe Enter first point: 10 20 Enter second point: 3 5 First point: (10,20) Second point: (3,5) The Ohio State University

  26. (Major) Problems with C-style Strings const int MAX_LENGTH(20); char s[MAX_LENGTH] = { 'H', 'e', 'l', 'l', 'o', '\0'}; cout << "String = " << s << endl; • Forgetting to end the string with ‘\0’; • Not allocating enough memory for the string; • How do you add an element to a string? • How do you delete an element from a string? • How do you concatenate two strings? The Ohio State University

  27. C++ Strings The Ohio State University

  28. C++ class string • C++ class string requires: #include <string> using namespace std; • To create a variable of type string, simply: string lastName; • Assignment, as always is the same: lastName = “Marx”; • Or combine the two with an initialization: string lastName(“Marx”); Or string lastname = “Marx”; The Ohio State University

  29. String Operators: Assignment • Assignment (=): As with before, assign a string to a variable of type string. string lastName(“Marx”), anothername; anothername = lastName; • Both now hold “Marx” The Ohio State University

  30. String Operators: Concatentation • Concatenation (+): Puts a string on the end of another. string firstName(“Groucho”); string lastName(“Marx”); string fullname = firstName + lastname; The Ohio State University

  31. concatString.cpp #include <iostream> #include <string> // <--------- Note using namespace std; int main() { string name1("Groucho“), name2(“Harpo”); string lastName("Marx“); string fullName1 = name1 + lastName; string fullName2 = name2 + lastName; cout << fullName1 << endl; cout << fullName2 << endl; The Ohio State University

  32. concatString.cpp #include <iostream> #include <string> // <--------- Note ... { string name1("Groucho“), name2(“Harpo”); string lastName("Marx“); string fullName1 = name1 + lastName; string fullName2 = name2 + lastName; cout << fullName1 << endl; cout << fullName2 << endl; > concatString.exe GrouchoMarx HarpoMarx The Ohio State University

  33. concatString2.cpp #include <iostream> #include <string> // <--------- Note using namespace std; int main() { string name1("Groucho“), name2(“Harpo”); string lastName("Marx“); // separate first and last names with a blank string fullName1 = name1 + " " + lastName; string fullName2 = name2 + " " + lastName; cout << fullName1 << endl; cout << fullName2 << endl; The Ohio State University

  34. concatString2.cpp #include <iostream> #include <string> // <--------- Note ... { string name1("Groucho“), name2(“Harpo”); string lastName("Marx“); // separate first and last names with a blank string fullName1 = name1 + " " + lastName; string fullName2 = name2 + " " + lastName; cout << fullName1 << endl; cout << fullName2 << endl; > concatString.exe Groucho Marx Harpo Marx The Ohio State University

  35. C++ String I/O The Ohio State University

  36. Input/Output with Strings • I/O with Strings are as before: string lastName; cout << “Please enter your last name: “; cin >> lastName; // get the last name cout << “Your last name is “ << lastName; The Ohio State University

  37. getName.cpp #include <iostream> #include <string> using namespace std; int main() { string firstName, lastName, fullName; cout << "Enter your first name: "; cin >> firstName; cout << "Enter your last name: "; cin >> lastName; // concatenate fullName = firstName + " " + lastName; cout << "Your name is: " << fullName << endl; The Ohio State University

  38. getName.cpp string firstName, lastName, fullName; cout << "Enter your first name: "; cin >> firstName; cout << "Enter your last name: "; cin >> lastName; // concatenate fullName = firstName + " " + lastName; cout << "Your name is: " << fullName << endl; > getName.exe Enter your first name: Groucho Enter your last name: Marx Your name is: Groucho Marx The Ohio State University

  39. getName2.cpp #include <iostream> #include <string> using namespace std; int main() { string fullName; cout << "Enter your full name: "; cin >> fullName; cout << "Your name is: " << fullName << endl; return 0; } The Ohio State University

  40. getName2.cpp ... string fullName; cout << "Enter your full name: "; cin >> fullName; cout << "Your name is: " << fullName << endl; ... > getName2.exe Enter your full name: Groucho Marx Your name is: Groucho The Ohio State University

  41. Input/Output with Strings • A common problem with reading strings from user input is that it could contain white spaces. • cin uses white space (e.g. space, tab, newline) as a delimiter between inputs; cin >> fullName; > getName2.exe Enter your full name: Groucho Marx Your name is: Groucho The Ohio State University

  42. String I/O: getline() • Fortunately, the string class let’s us get around this with the getline() function. • Syntax: getline(source, destination) • source is the source of the string. In our case, we want cin here. • destination is the string variable where we want the string to be read into. The Ohio State University

  43. String I/O: getline() • We can fix our code by rewriting it as follows: string fullname; cout << “Enter your full name: ”; getline(cin, fullname); The Ohio State University

  44. getName3.cpp #include <iostream> #include <string> using namespace std; int main() { string fullName; cout << "Enter your full name: "; getline(cin, fullName); // <--------- Note cout << "Your name is: " << fullName << endl; return 0; } The Ohio State University

  45. getName3.cpp ... cout << "Enter your full name: "; getline(cin, fullName); // <--------- Note cout << "Your name is: " << fullName << endl; ... > getName3.exe Enter your full name: Groucho Marx Your name is: Groucho Marx > getName3.exe Enter your full name: Groucho G. Marx III Your name is: Groucho G. Marx III The Ohio State University

  46. getName3.cpp ... cout << "Enter your full name: "; getline(cin, fullName); // <--------- Note cout << "Your name is: " << fullName << endl; ... > getName3.exe Enter your full name: Groucho Marx Your name is: Groucho Marx > getName3.exe Enter your full name: Your name is: The Ohio State University

  47. literalError.cpp (BAD CODE) ... int main() { char firstName[10], lastName[10]; cout << "Enter first name: "; // DO NOT DO THIS. THIS IS VERY, VERY BAD! cin >> firstName; cout << "Enter last name: "; // DO NOT DO THIS. THIS IS VERY, VERY BAD! cin >> lastName; cout << "Your name is: " << firstName << " " << lastName << endl; return 0; } The Ohio State University

  48. ... char firstName[10], lastName[10]; cout << "Enter first name: "; // DO NOT DO THIS. THIS IS VERY, VERY BAD! cin >> firstName; cout << "Enter last name: "; // DO NOT DO THIS. THIS IS VERY, VERY BAD! cin >> lastName; cout << "Your name is: " << firstName << " " << lastName << endl; ... > literalError.exe Enter first name: John Enter last name: MacGhilleseatheanaich Your name is: naich MacGhilleseatheanaich > The Ohio State University

  49. C++ String Processing The Ohio State University

  50. str[k] • s[k] represents the k’th character in string s: string s(“Hello World”); // the character ‘H’ will be output. cout << s[0] << endl; // the character ‘W’ will be output. cout << s[6] << endl; The Ohio State University

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