1. Instructor: Dr. Michael Geiger Spring 2019 Lecture 6: Strings
EECE.3220 Data Structures
Instructor:
Dr. Michael Geiger
Spring 2019
Lecture 6:
Strings

2. Announcements/reminders
Program 1 due Friday, 2/8
All programs to be submitted via Blackboard
Submit a single .zip file containing all files for this assignment
Additional instructor support for course
Grader: Shubham Tikare
Office hours: Tues 9-11 AM, Ball 301E (ECE Conf Rm)
Tutor: Felipe Loera
Hours available on CLASS site (link also on home page)
6/12/2019
Data Structures: Lecture 6

3. Data Structures: Lecture 6
Lecture outline
Review
Output manipulators
Other input methods
C++ strings
6/12/2019
Data Structures: Lecture 6

4. Review: Output manipulators
setprecision: change number of digits displayed to the right of the decimal point
fixed: fixed format (no scientific notation)
showpoint: force decimal point (and trailing zeros) to be shown
Default behavior (without showpoint) is to not show trailing zeros
Default precision (with showpoint) is 6
Reset with noshowpoint
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Data Structures: Lecture 6

5. Clarifying manipulators
showpoint does not imply fixed format
Could be fixed point, could be scientific notation
Scientific notation used if
precision < # digits before decimal point
Default behavior: precision = sig. figures
After showpoint: precision = digits after point
Clearing fixed flag: defaultfloat
There aren’t just two options …
… but we’re not going to discuss the other ones
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Data Structures: Lecture 6

6. Review: Characters and input
Input (cin) streams
Use cin to read values into variables
E.g., cin >> x;
Skips whitespace characters
Input value must be compatible with type of x
Reading n characters: cin.get(buffer, n);
Reading 1 character: cin.get(ch);
Reading an entire line (at most m characters): cin.getline(buffer, m)
May need cin.ignore(x) to skip characters
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Data Structures: Lecture 6

7. Standard Library Class string
Header <string>, namespace std
Basic uses:
Initialization: string s1( "hi" );
Input/output (as in cout << s1)
Assignment: s1 = "hi";
Can also use:
Relational operators: ==, !=, >=, >, <=, <
Perform char-by-char comparison using ASCII values
Concatenation: +=
E.g.: s1 += “lly”  s1 = “hilly”
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Data Structures: Lecture 6

8. Standard Library Class string (Cont.)
Substring member function substr
s1.substr( 0, 14 );
Starts at location 0, gets 14 characters
s1.substr( 15 );
Substring beginning at location 15, to the end
Overloaded []
Access one character
No range checking (if subscript invalid)
Member function at
Accesses one character
Example
s1.at( 10 );
Has bounds checking, throws an exception if subscript is invalid
Member function empty
Returns true if no characters in string
Member function length
Returns number of characters in string
string s = “Hello”;  s.length() = 5
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Data Structures: Lecture 6

9. Example: Strings & functions
int main() { string s1( "happy" ); string s2( " birthday" ); string s3; // test overloaded equality and relational operators cout << "s1 is \"" << s1 << "\"; s2 is \"" << s2 << "\"; s3 is \"" << s3 << '\"' << "\n\nThe results of comparing s2 and s1:" << "\ns2 == s1 yields " << ( s2 == s1 ? "true" : "false" ) << "\ns2 != s1 yields " << ( s2 != s1 ? "true" : "false" ) << "\ns2 > s1 yields " << ( s2 > s1 ? "true" : "false" ) << "\ns2 < s1 yields " << ( s2 < s1 ? "true" : "false" ) << "\ns2 >= s1 yields " << ( s2 >= s1 ? "true" : "false" ) << "\ns2 <= s1 yields " << ( s2 <= s1 ? "true" : "false" );
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Data Structures: Lecture 6

10. Data Structures: Lecture 6
Example (cont.)
Output from previous slide: s1 is “happy”; s2 is “ birthday”; s3 is “” The results of comparing s1 and s2: s2 == s1 yields false s2 != s1 yields true s2 > s1 yields false s2 < s1 yields true s2 >= s1 yields false s2 <= s1 yields true
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Data Structures: Lecture 6

11. Data Structures: Lecture 6
Example (cont.)
// test string member function empty cout << "\n\nTesting s3.empty():" << endl; if ( s3.empty() ) { cout << "s3 is empty; assigning s1 to s3;" << endl; s3 = s1; // assign s1 to s3 cout << "s3 is \"" << s3 << "\""; } // end if // test overloaded string concatenation operator cout << "\n\ns1 += s2 yields s1 = "; s1 += s2; // test overloaded concatenation cout << s1; // test concatenation operator with C-style string cout << "\n\ns1 += \" to you\" yields" << endl; s1 += " to you"; cout << "s1 = " << s1 << "\n\n";
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Data Structures: Lecture 6

12. Data Structures: Lecture 6
Example (cont.)
Output from previous slide: Testing s3.empty(): s3 is empty; assigning s1 to s3; s3 is “happy” s1 += s2 yields s1 = happy birthday s1 += “ to you” yields s1 = happy birthday to you
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Data Structures: Lecture 6

13. Data Structures: Lecture 6
Example (cont.)
// test string member function substr cout << "The substring of s1 starting at location 0 for\n" << "14 characters, s1.substr(0, 14), is:\n" << s1.substr( 0, 14 ) << "\n\n"; // test substr "to-end-of-string" option cout << "The substring of s1 starting at\n" << "location 15, s1.substr(15), is:\n" << s1.substr( 15 ) << endl; // test using subscript operator to create lvalue s1[ 0 ] = 'H'; s1[ 6 ] = 'B'; cout << "\ns1 after s1[0] = 'H' and s1[6] = 'B' is: " << s1 << "\n\n"; // test subscript out of range with string member function "at" cout << "Attempt to assign 'd' to s1.at( 30 ) yields:" << endl; s1.at( 30 ) = 'd'; // ERROR: subscript out of range return 0; } // end main
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Data Structures: Lecture 6

14. Data Structures: Lecture 6
Example (cont.)
Output from previous slide: The substring of s1 starting at location 0 for 14 characters, s1.substr(0, 14), is: happy birthday The substring of s1 starting at location 15, s1.substr(15), is: to you s1 after s1[0] = ‘H’ and s1[6] = ‘B’ is: Happy Birthday to you Attempt to assign ‘d’ to s1.at(30) yields abnormal program completion
6/12/2019
Data Structures: Lecture 6

15. Data Structures: Lecture 6
Final notes
Next time
Algorithmic complexity intro
Reminders:
Program 1 due Friday, 2/8
All programs to be submitted via Blackboard
Submit a single .zip file containing all files for this assignment
Additional instructor support for course
Grader: Shubham Tikare
Office hours: Tues 9-11 AM, Ball 301E (ECE Conf Rm)
Tutor: Felipe Loera
Hours available on CLASS site (link also on home page)
6/12/2019
Data Structures: Lecture 6