1. Bjarne Stroustrup www.stroustrup.com/Programming
Chapter 4 Computation
Bjarne Stroustrup

2. Abstract basics of computation Selection, Iteration, Function, Vector
Expressions
select between two alternative actions (“selection”)
how to iterate over a series of values (“iteration”)
I’ll also show how a particular sub-computation can be named and specified separately as a function.
To be able to perform more realistic computations, I will introduce the vector type to hold sequences of values.
Selection, Iteration, Function, Vector
Stroustrup/Programming

3. Overview Computation Language constructs and ideas
What is computable? How best to compute it?
Abstractions, algorithms, heuristics, data structures
Language constructs and ideas
Sequential order of execution
Expressions and Statements
Selection
Iteration
Functions
Vectors
Stroustrup/Programming

4. Computation Code, often messy, often a lot of code (input) data
(output) data
data
Input: from keyboard, files, other input devices, other programs, other parts of a program
Computation – what our program will do with the input to produce the output.
Output: to screen, files, other output devices, other programs, other parts of a program
Stroustrup/Programming

5. Computation Our job is to express computations
Correctly
Simply
Efficiently
One tool is called abstraction, which provides a higher-level concept that hides detail
cin is an abstraction of keyboard device
Device driver handles details about hardware interrupt, buffering, …
cout
data type such as int, double, are abstractions of memory
Stroustrup/Programming

6. Computation (cont’d) One tool is called Divide and Conquer
to break up big computations into many smaller ones
Like assembly line, organization, building lego toys
Organization of data is often the key to good code
Input/output formats
Protocols
Data structures
A pizza restaurant system that keeps all transaction records
Note the emphasis on structure and organization
You don’t get good code just by writing a lot of statements
Stroustrup/Programming

7. Language features
Each programming language feature exists to express a fundamental idea
+ : addition
* : multiplication
if (expression) statement else statement ; selection
while (expression) statement ; iteration
f(x); function/operation …
We combine language features to create programs
Stroustrup/Programming

8. You already know most of this
You know how to do arithmetic
d = a+b*c
You know how to select
“if this is true, do that; otherwise do something else ”
You know how to “iterate”
“do this until you are finished”
“do that 100 times”
You know how to do functions
“go ask Joe and bring back the answer”
“hey Joe, calculate this for me and send me the answer”
What we learn here is mostly just vocabulary and syntax for what you already know
Stroustrup/Programming

9. Expressions An expression computes a value from a number of operands
Most basic building block of programs
Simplest expression: a literal value, name of variables
10, ‘a’, 3.24, “Hello world!\n”
total_due, change, …
More complicated expressions: made out of operators and operands
Operators specify what is to be done, +, *, =, /, …
Operands specify the data for the operators to work with
Stroustrup/Programming

10. Expressions
// compute area: int length = 20; // the simplest expression: a literal (here, 20) // (here used to initialize a variable) int width = 40; int area = length*width; // a multiplication int average = (length+width)/2; // addition and division The usual rules of precedence apply: a*b+c/d means (a*b)+(c/d) and not a*(b+c)/d. If in doubt, parenthesize. If complicated, parenthesize. Don’t write “absurdly complicated” expressions: a*b+c/d*(e-f/g)/h+7 // too complicated Choose meaningful names.
Stroustrup/Programming

11. Constant expressions
Three types of constant expressions: literal value, named constant, an expression with only constant operands
3.1415, 15.39, 19.39
const double PRICE_12_PIZZA = 15.39;
double total = num12*PRICE_12_PIZZA +
num14*PRICE_14_PIZZA;
const int max=18;
max+2; //this is a constant expression
Stroustrup/Programming

12. Assignment expression
int average=20;
average = average/2;
average on left-hand side and right-hand side of = interpreted differently
Left-hand: means “the object named average”, “lvalue of average”
Right-hand: means “the value of the object named by average”, “the value of average”, “rvalue of average”
Left-hand operand of assignment operator, =, needs to be a variable
10=a; // compilation error
“error: lvalue required as left operand of assignment”
Stroustrup/Programming

13. Data types & OPERATORS Integer types: short, int, long
Arithmetic operators: +, -, *, /, % (remainder)
Relational operators: < (less than), > (greater than), <=, >=
Floating-point types: e.g., float, double (e.g., and e3)
arithmetic operators: +, -, *, /
Boolean type: bool (true and false)
Equality operators: = = (equal), != (not equal)
Logical operators: && (and), || (or), ! (not)
Character type: char (e.g., 'a', '7', and
Stroustrup/Programming

14. Integer division and module operation
Integer types: short, int, long
Arithmetic operators: +, -, *, /, % (remainder)
All above operations evaluate to an integer
4/3, 123 % 2, …
Integer division: fraction part is thrown away
4/3 = 1
23/45 = 0
Module operator: %
a%b evaluates to the remainder when a is divided by b
5 % 2 is 1 , 4 % 2 is 0
23 % 10 is 3 ,…
Stroustrup/Programming

15. Integer/float arithmetic
Fahrenheit to Celsius
(°F - 32) x 5/9 => °C
How to implement it in C++ code?
Stroustrup/Programming

16. Exercises What’s the value of the following expressions?
1.0+13/4 , (1.0+13)/4
123 % 10
How to express using C++?
double x1=
double x2=
Recall function sqrt(t) return square root of t
How to find the 10th digit of an integer?
E.g., 10th digit of 342 is 4
Stroustrup/Programming

17. Concise Operators
For many binary operators, there are (roughly) equivalent more concise operators
For example
a += c means a = a+c
a *= scale means a = a*scale
++a means a += 1
or a = a+1
“Concise operators” are generally better to use
(clearer, express an idea more directly)
Stroustrup/Programming

18. Note: = is used for assignment
Comparison operators
Used to compare numbers and strings, evaluate to a bool value (true or false)
C++ Math Notation Description
>> > Greater than,
>= ≥ Greater than or equal
< < Less than
<= ≤ Less than or equal
== = Equal
!= ≠ Not equal
Note: = is used for assignment
== tests for equality
Stroustrup/Programming

19. Data types & OPERATORS Integer types: short, int, long
Arithmetic operators: +, -, *, /, % (remainder)
Relational operators: < (less than), > (greater than), <=, >=, ==, !=
Floating-point types: e.g., float, double (e.g., and e3)
arithmetic operators: +, -, *, /
Boolean type: bool (true and false)
Logical/Boolean operators: && (and), || (or), ! (not)
Character type: char (e.g., 'a', '7', and
Stroustrup/Programming

20. Data Type: bool an bool variable has two possible value: true or false
Useful for storing a value to be used later:
bool discounted =
(country == "USA" && weight <= 1);
...
if (discounted) ...
Also makes the code more legible
Stroustrup/Programming

21. Data Type: bool in C++ any nonzero value “evaluates” to true
if (n) // if (n!=0)
cout << “n is not zero \n”;
Don't do this:
if (x = 7) ... // a logic error!
Will always be true
x will have the value 7 afterwards
Stroustrup/Programming

22. Boolean Operations
Boolean operators (after George Boole) have Boolean expressions as operands
combine conditions into larger, more complex Boolean expressions
Two binary operators:
&& logical and
|| Logical or
One uniary operators:
! Logic not
Stroustrup/Programming

23. Boolean Operations (examples)
Following test is true only when both country is "USA", and the weight is < 1
if (country == "USA" && weight <= 1)
shipping_charge = 2.50;
following test is true if state is either "HI" or "AK":
if (state == "HI" || state == "AK")
shipping_charge = 10.00;
Stroustrup/Programming

24. Boolean Operations (not operator)
The ! operator (said "not") inverts the value of a Boolean expression (unary operator)
! (n==0) is the same as (n!=0)
! (n>=0) is same as (n<0)
! (k>m) is same as ?
Prefer the simpler expressions
Stroustrup/Programming

25. Common Error: Multiple Relational Operators
x=-10.0;
if (-0.5 <= x <= 2.5) // a logic error
Makes sense in mathematics, testing whether x falls within the range
C++ interprets it as follows:
-0.5 <= x evaluates to true (1) or false (0)
Compare Boolean value to double value of 2.5, always true
Needs to be done this way:
if (-0.5 <= x && x <= 0.5) ...
Stroustrup/Programming

26. Boolean Operations (summary)
A && B
true
false A B
A || B
true
false A !A
True
False
true
Stroustrup/Programming

27. Boolean Operations (lazy evaluation)
&& and || operators are evaluated lazily
Operands are evaluated left-to-right
Evaluation ends as soon as the truth value is determined
Given X is true and Y is false:
X || Y is true; Y is not evaluated (there is no need …)
Y && X is false; X is not evaluated
This is quite handy:
(n > 0) && (tot/n < 0.9)
Stroustrup/Programming

28. Exercise What the value of following boolean expression? int x=10;
bool b1 = (x % 2 == 0);
bool b2 = (x>10 || x!=2);
bool b3 = ( (x-2)<8 );
Stroustrup/Programming

29. Statements A statement is
an expression followed by a semicolon, a = b;
a declaration, double d2 = 2.5;
a “control statement” that determines the flow of control
if (x == 2) y = 4;
while (cin >> number) numbers.push_back(number);
int average = (length+width)/2;
return x;
You may not understand all of these just now, but you will …
Stroustrup/Programming

30. Selection Sometimes we must specify a conditional process
if number of 12-inch pizzas is greater than 0 , display the number and price
if (num12 > 0)
cout <<″12-inch pizza\t\t″
<<num12<<″\t″
<<num12*PRICE_12_PIZZA <<″\n″;
Syntax is
if (condition)
statement
//statement is executed only if condition is true
true
condition
statement
false
Next statement
in program
Stroustrup/Programming

31. Selection if (a<b) // Note: No semicolon here
select between alternatives
E.g, to identify larger of two values:
if (a<b) // Note: No semicolon here
max = b;
else // Note: No semicolon here
max = a;
syntax is
if (condition)
statement-1 // if condition is true, do statement-1
else
statement-2 // if not, do statement-2
false
true
condition
Statement-1
Statement-2
Next statement
in program
Stroustrup/Programming

32. Block statement
if (condition)
statement //if condition is true, do statement
statement-1 // if condition is true, do statement-1
else
statement-2 // if not, do statement-2
Statement can be a block statement, i.e., a sequence of statements enclosed by { and }
if (num_12 < 0) {
cout <<“Invalid input\n”;
return -1; //exit the program with a -1 return value }
Stroustrup/Programming

33. Next half
Stroustrup/Programming

34. Rules of operator precedence
Operators in parentheses evaluated first
Nested/embedded parentheses
Operators in innermost pair first
Multiplication, division, modulus applied next
Operators applied from left to right
Addition, subtraction applied last
CS1600 Xiaolan Zhang
Fall 2010

35. Programming errors Syntax errors (or compilation errors)
Mistyping a keyword
Variables not declared
Missing semicolons, …
Runtime errors
Not captured by compiler, execution aborted
E.g. divide by zero, accessing wrong memory location, …
Avoid them by checking input, …
Logic errors
Program executed normally to the end, but outcome is wrong
E.g. int area = r*r*3.1415;

36. Question Question : Which statement is correct , A or B ?
int integerOne = 1;
double doubleOne = 2.5;
int sumOne = integerOne + doubleOne; //A
double sumTwo = integerOne + doubleOne; //B
Which statement is correct , A or B ?
CS1600 Xiaolan Zhang

37. Output Statement With Expression
Variables or expressions could be inserted into output statement, its value is printed out.
Long output statement could be broken into multiple lines.
Example:
std::cout << “sum is ” << sum
<< “. bye-bye! \n”;
std::cout << “sum is ”
<< number1 + number2 ;
CS1600 Xiaolan Zhang

38. INT, double, float, …
Stroustrup/Programming

39. Data type int
Representing whole numbers, i.e., those numbers that have no decimal parts
For counting number of people, classrooms, stars,…
In C/C++,
int data type is 4 byte long (32 bits)
Can store values from -2,147,483,648 to 2,147,483,647
long long: 8 byte long (64 bits)
-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

40. Floating point type For storing values with decimal parts, real values
E.g., , 15.39, , sqrt(2),
C/C++ provides two floating point type:
float and double
float: usually 32 bits long
Can store values within range: 3.4 e-38, 3.4e+38
has a precision of 7 digits
type double: 64 bits long
Can store value within range: 1.7e308, 1.7e308
15 digits precision
Stroustrup/Programming

41. If change double to float,
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double a= e10; // the literal constant has 8 significant digits
cout <<"a=" << setprecision(10) << a<<endl; }
Output:
a= e+10 //double can represent the value accurately
If change double to float,
a= e+10 //float cannot
Stroustrup/Programming

42. #include <iomanip> int main() { double a; int n; cout <<"Enter a:"; cin >> a; cout <<"a's value is " << a << “\n"; }
test_double.cpp
Try following input:
30, output 30
30.00, output 30
2e310, output e+308
, output
Value overflow!
By default, cout outputs
a double value with up to
6 significant digits
Stroustrup/Programming

43. double data type represents a number
If enter value
output:
If value entered is:
output is:
e-08
output is :
e+26
e+00
double data type represents a number
approximately, the precision is 15
significant digits. (sometimes you get lucky ).
#include <iomanip> int main() { double a; cout <<"Enter a:"; cin >> a; cout <<"a's value is " << setprecision (20) // display value up to 20 // significant digits << a <<"\n"; }
test_double2.cpp
Stroustrup/Programming

44. Significant digits
Significant digits of a number: digits that carry meaning contributing to its precision.
this includes all digits except leading zeros 
double data type guarantees to represents a number accurately up to 15 significant digits, i.e., it has a precision of 15
float data type guarantees to represents a number accurately up to 7 significant digits, i.e., it has a precision of 7
long double …
Stroustrup/Programming

45. significant DIGITS All non-zero digits are considered significant.
91 has two (9 and 1), while has five (1, 2, 3, 4 and 5).
Zeros appearing between two non-zero digits are significant
has five: 1, 0, 1, 1 and 2.
Leading zeros are not significant
has two significant figures: 5 and 2.
Trailing zeros in a number are significant.
has six : 1, 2, 2, 3, 0 and 0.
still has only six (the zeros before the 1 are not significant)
has five significant figures
12.23 vs
Stroustrup/Programming

46. Precision of floating type
Precision: the number of significant digits the data type can store without loss of information
E.g …33
There are 100 number of 3.
Both double and type use finite amount of memory, cannot store all possible real value exactly

47. Output: If change to float type,
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double a= e10; // the literal constant has 8 significant digits
cout <<"a=" << setprecision(10) << a<<endl; }
Output:
a= e+10 //double can represent the value accurately
If change to float type,
a= e+10 //float cannot
Stroustrup/Programming

48. [zhang@storm Codes]$ ./a.out
double change= *1; cout <<"change due" << fixed <<change<<endl; int d= change; cout <<"d=" << d <<endl; int q = (change-d)/0.25; cout <<"q=" << q <<endl; int dm = (change-d-q*0.25)/0.1; cout <<"dm=" << dm <<endl; int n = (change-d-q*0.25-dm*0.1)/0.05; cout <<"n=" << n <<endl; int p = (change-d-q*0.25-dm*0.1-n*0.05)/0.01; cout <<"Right hand side" << setprecision(15) << fixed << (change-d-q*0.25-dm*0.1-n*0.05)/0.01 <<endl; cout <<"p=" << p <<endl;
Give Change problem
Codes]$ ./a.out
change due
d=24
q=2
dm=1
n=0
Right hand side
p=1
Stroustrup/Programming

49. 49
Solution
Better solution: use int to store
money amount (measured in cents)
#include <math.h>
int dollar = floor(change);
int p = round(change-d-q*0.25-dm*0.1-n*0.05)/0.01;
int cents = round(change);
floor(double x): return the largest integral value that is not greater than x
round (double x): round x to the nearest integer
round (0.5)=1, round (56.0)=56

50. Back to selection statement, i.e., IF/else statement
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51. Nested Branches
Often necessary to nest an if/else statement inside another, to decide across several categories
Stroustrup/Programming

52. Demo Write embedded if/else statements Exercise
Leap year testing logic
Stroustrup/Programming

53. Multiple alternative if (richter>=8.0)
cout <<“most structure fall\n”;
else {
if (richter>=7.0)
cout <<“Many buildings destroyed\n”;
else {
if (richter >=6.0)
cout <<“Many building consi…\n”;
if (richter>=4.5)
cout <<“damage to ..\n”; }
cout <<“No des…\n”;
Stroustrup/Programming

54. Multiple alternative if (richter>=8.0) if (richter>=8.0)
cout <<“most structure fall\n”;
else
if (richter>=7.0)
cout <<“Many buildings destroyed\n”;
if (richter >=6.0)
cout <<“Many building consi…\n”;
if (richter>=4.5)
cout <<“damage to ..\n”;
cout <<“No des…\n”;
if (richter>=8.0)
cout <<“most structure fall\n”;
else {
if (richter>=7.0)
cout <<“Many buildings destroyed\n”;
else {
if (richter >=6.0)
cout <<“Many building consi…\n”;
if (richter>=4.5)
cout <<“damage to ..\n”; }
cout <<“No des…\n”;
Stroustrup/Programming

55. Multiple alternatives
if (richter >= 8.0) cout << "Most structures fall"; else if (richter >= 7.0) cout << "Many buildings destroyed"; else if (richter >= 6.0) cout << "Many buildings …"; else if (richter >= 4.5) cout << "Damage to …"; else cout << "Generally no damage";
if (richter>=8.0)
cout <<“most structure fall\n”;
else
if (richter>=7.0)
cout <<“Many buildings destroyed\n”;
if (richter >=6.0)
cout <<“Many building consi…\n”;
if (richter>=4.5)
cout <<“damage to ..\n”;
cout <<“No des…\n”;
Stroustrup/Programming

56. Exercise
Implement a menu selection, where program prompt user to select diff. action based on input:
Enter a simple arithmetic expression (+,-,*,/,%):
Result is: 36
Hint:
char op;
cin >> num1 >> op >> num2;
//test whether op is equal to ‘+’, ‘-’,’*’,’/’.
Stroustrup/Programming

57. Summary Expression, operators Statement
Declaration statement
Expression statement
if statement, return statement
cout, cin, statement
Difference between expression and statement?
Statement ends with ;
Expression can be used in cout
cout <<“Total is: “ << n1*p1+n2*p2 <<“\n”;
cout <<“total is: “ << double total <<“\n”; //not an expression
Stroustrup/Programming

58. Iteration (while loop)
The world’s first “real program” running on a stored- program computer (David Wheeler, Cambridge, May 6, 1949)
// calculate and print a table of squares 0-99:
int main() {
int i = 0;
while (i<100) {
cout << i << '\t' << square(i) << '\n';
++i ; // increment i }
// (No, it wasn’t actually written in C++ .)
Stroustrup/Programming

59. Iteration (while loop)
What it takes
A loop variable (control variable); here: i
Initialize the control variable; here: int i = 0
A termination criterion; here: if i<100 is false, terminate
Increment the control variable; here: ++i
Something to do for each iteration; here: cout << …
int i = 0;
while (i<100) {
cout << i << '\t' << square(i) << '\n';
++i ; // increment i }
Stroustrup/Programming

60. Iteration (for loop) Another iteration form: for loop
You can collect all the control information in one place, at the top, where it’s easy to see
for (int i = 0; i<100; ++i) {
cout << i << '\t' << square(i) << '\n'; }
That is,
for (initialize; condition ; increment )
controlled statement
Note: what is square(i)?
Stroustrup/Programming

61. Functions But what was square(i)? A call of the function square()
int square(int x) {
return x*x; }
We define a function when we want to separate a computation because it
is logically separate
makes the program text clearer (by naming the computation)
is useful in more than one place in our program
eases testing, distribution of labor, and maintenance
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62. Control Flow int main() { i=0; while (i<100) square(i) }
int square(int x) {
return x * x; }
i<100
i==100
Stroustrup/Programming

63. Functions is an example of Our function int square(int x) {
return x*x; }
is an example of
Return_type function_name ( Parameter list )
// (type name, etc.)
// use each parameter in code
return some_value; // of Return_type
Stroustrup/Programming

64. Another Example
Earlier we looked at code to find the larger of two values. Here is a function that compares the two values and returns the larger value.
int max(int a, int b) // this function takes 2 parameters {
if (a<b)
return b;
else
return a; }
int x = max(7, 9); // x becomes 9
int y = max(19, -27); // y becomes 19
int z = max(20, 20); // z becomes 20
Stroustrup/Programming

65. Data for Iteration - Vector
To do just about anything of interest, we need a collection of
data to work on. We can store this data in a vector. For example:
// read some temperatures into a vector:
int main() {
vector<double> temps; // declare a vector of type double to store // temperatures – like 62.4
double temp; // a variable for a single temperature value
while (cin>>temp) // cin reads a value and stores it in temp
temps.push_back(temp); // store the value of temp in the vector
// … do something … }
// cin>>temp will return true until we reach the end of file or encounter
// something that isn’t a double: like the word “end”
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66. Vector Vector is the most useful standard library data type v: 5 1 4 2
a vector<T> holds an sequence of values of type T
Think of a vector this way
A vector named v contains 5 elements: {1, 4, 2, 3, 5}:
size() v: 5
v[0]
v[1]
v[2]
v[3]
v[4] 1 4 2 3 5
v’s elements:
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67. Vectors
vector<int> v; // start off empty v.push_back(1); // add an element with the value 1 v.push_back(4); // add an element with the value 4 at end (“the back”) v.push_back(3); // add an element with the value 3 at end (“the back”) v[0] v[1] v[2] v: 1 1 v: 2 1 4 v: 3 1 4 3 v:
Stroustrup/Programming

68. Vectors
Once you get your data into a vector you can easily manipulate it:
// compute mean (average) and median temperatures:
int main() {
vector<double> temps; // temperatures in Fahrenheit, e.g. 64.6
double temp;
while (cin>>temp) temps.push_back(temp); // read and put into vector
double sum = 0;
for (int i = 0; i< temps.size(); ++i) sum += temps[i];
// sums temperatures
cout << "Mean temperature: " << sum/temps.size() << endl;
sort(temps.begin(),temps.end());
cout << "Median temperature: " << temps[temps.size()/2] << endl; }
Stroustrup/Programming

69. Combining Language Features
You can write many new programs by combining language features, built-in types, and user-defined types in new and interesting ways.
So far, we have
Variables and literals of types bool, char, int, double
vector, push_back(), [ ] (subscripting)
!=, ==, =, +, -, +=, <, &&, ||, !
max( ), sort( ), cin>>, cout<<
if, for, while
You can write a lot of different programs with these language features! Let’s try to use them in a slightly different way…
Stroustrup/Programming

70. Example – Word List
// “boilerplate” left out vector<string> words; string s; while (cin>>s && s != "quit") // && means AND words.push_back(s); sort(words.begin(), words.end()); // sort the words we read for (int i=0; i<words.size(); ++i) cout<<words[i]<< "\n"; /* read a bunch of strings into a vector of strings, sort them into lexicographical order (alphabetical order), and print the strings from the vector to see what we have. */
Stroustrup/Programming

71. Word list – Eliminate Duplicates
// Note that duplicate words were printed multiple times. For // example “the the the”. That’s tedious, let’s eliminate duplicates: vector<string> words; string s; while (cin>>s && s!= "quit") words.push_back(s); sort(words.begin(), words.end()); for (int i=1; i<words.size(); ++i) if(words[i-1]==words[i]) “get rid of words[i]” // (pseudocode) for (int i=0; i<words.size(); ++i) cout<<words[i]<< "\n"; // there are many ways to “get rid of words[i]”; many of them are messy // (that’s typical). Our job as programmers is to choose a simple clean // solution – given constraints – time, run-time, memory.
Stroustrup/Programming

72. Example (cont.) Eliminate Words!
// Eliminate the duplicate words by copying only unique words: vector<string> words; string s; while (cin>>s && s!= "quit") words.push_back(s); sort(words.begin(), words.end()); vector<string>w2; if (0<words.size()) { // Note style { } w2.push_back(words[0]); for (int i=1; i<words.size(); ++i) if(words[i-1]!=words[i]) w2.push_back(words[i]); } cout<< "found " << words.size()-w2.size() << " duplicates\n"; for (int i=0; i<w2.size(); ++i) cout << w2[i] << "\n";
Stroustrup/Programming

73. Algorithm We just used a simple algorithm
An algorithm is (from Google search)
“a logical arithmetical or computational procedure that, if correctly applied, ensures the solution of a problem.” – Harper Collins
“a set of rules for solving a problem in a finite number of steps, as for finding the greatest common divisor.” – Random House
“a detailed sequence of actions to perform or accomplish some task. Named after an Iranian mathematician, Al-Khawarizmi. Technically, an algorithm must reach a result after a finite number of steps, …The term is also used loosely for any sequence of actions (which may or may not terminate).” – Webster’s
We eliminated the duplicates by first sorting the vector (so that duplicates are adjacent), and then copying only strings that differ from their predecessor into another vector.
Stroustrup/Programming

74. Ideal
Basic language features and libraries should be usable in essentially arbitrary combinations.
We are not too far from that ideal.
If a combination of features and types make sense, it will probably work.
The compiler helps by rejecting some absurdities.
Stroustrup/Programming

75. The next lecture
How to deal with errors
Stroustrup/Programming