C++ 101 Midterm 3 Cheat Sheet

A cheat sheet in English by sadieweaver

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istream ostream

friend ostream& operator<<(ostream& out, room& r) { out << “Width:”  <<  r.width << “, Length:” << r.length; return out; }

friend istream& operator>>(istream& in, room& r) { cout << “Enter width: “ << endl; in >> r.width; cout << “Enter length: “ < endl; in >> r.length; return in; }

Strings vs C-strings (ch8)

`#include <string>`	`#include <cstring>`
Reading in:
	>> stops reading at the first space
`string input;` `getline(cin, input);`	`char input[100]` `cin.getline(input, 100);`
`string s1;`	empty c-string: `char s[20] = "";`
Returning:
	returning c-strings: return type of pointer. `char* funct(){...return...}`
for both: make sure that if you return something in a function if it's a variable defined in the function that is was defined dynamically or is `static`.
Operations:
`s.length()` or `s.size()`	`strlen(s)` - s is a c-string cannot use .length() or .size()
`s2 = s1;`	`strcpy(s2, s1)` - copy s1 to s2
`s1 == s2;`	`strcmp(s1, s2) == 0;` - tests for equality
`s1 += s3`	`strcat(char* s1, const char* s2);`
string s to double `stod(s);`
`char* s` to `double`: `strtod(s, nullptr);`
Functions:
Random:
	c-strings have a null termination character '/0'. So to define a c-string to hold 20 it's `char input[21];`
same thing as >	c++ doesn't check indexes to validate if something is within bounds
`int n = 3; cout << (char)(n + '0') << endl;` prints 3.
`char c = 'D'; cout << (c - 'A') << endl;` prints 3.
`char name[100]; char* get_name() { . . . return _______________; }` return `name`

Constructors

Default: foo() no arguments
foo f1; or foo* f2 = new foo;

Conversion: foo(int i) one argument to be turned into the class object
foo f1(3); or foo* f2 = new foo(3);

General: foo(int x, int y) anything with more than one

Copy: foo(foo& f) pointer argument

Move: foo(foo&& f) double pointer

Constructor and Initializer List Examples

Choose the best C++ class named person that has: A private member field for the person’s first name; A private member field for the person’s last name; A private member field for the person’s age; and a public constructor:

class Person{ string first; string last; int age; 
public: person(string f, string l, int a) : first(f), last(l), age(a) {} };

UML: Student
-name: string
-gpa:double
+Student(n: string, g: double)

class Student
{private: 
string name;
double gpa;
public:
Student(string n, double g) : name(n), gpa(g) {} };

Write a single constructor that works as default, conversion, and general: UML fraction
-numerator:int
-denominator:int
+fraction(n: int, d:int)
(default values: n = 0, d = 1)

fraction(int n = 0, int d = 1) : numerator(n), denominator(d) {}

UML: Foo
-count:int
+running: bool (set running to true)
+Foo(a_count: int)
-my_helper(arg: int) : char

class Foo
{private: 
int count;
char my_helper(int arg)
public:
bool running = true;
Foo(int a_count) : count(a_count) {} };

Extras

Only technical difference between structures and classes:

features in classes are private by default, features in structures are public by default

Constructors name is

the same as the name of the class

Facts

+: public
-: private
#: protected
underlined:static

Auto: Stack
Dynamic: Heap

defining functions outside of a class: return-type class::function-name(arguments) with a prototype included in class file.

Member/Friend Summary

member/nonmbr	Implicit Args	Explicit Args
Unary Member:	1	0
Unary Friend:	0	1
Binary Mbr:	1	1
Binary Friend:	0	2

mbr/ nonmbr in and out a class

Mbr defined in the class

foo operator+(foo f){...}

Mbr defined out the class

foo foo::operator+(foo f){...}

Nonmbr defined in the class

friend foo operator+(foo f1, foo f2) {...}

Nonmbr defined out the class

foo operator+(foo f1, foo f2) {...}

Command-line

main function definition to allow a program to access command line arguments:
main(int argc, char* argv[])

A program is named "my_program" and is executed from the command line as my_program file1 file2 file3 file4 If the program is written in C++ and the arguments are passed in to main, what is the value of argc and what is stored in argv[2]?
argc = 5, argv[2] = file2

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