C++ Expressions and Working with User Data

cin object

Standard console input
b. Need to add #include <iostream> for it to work
c. Reads input from keyboard
d. Use >> to set input from cin to a variable, as in:
cin >> your_variable (like your_variable = “my cin input”)
e. Cin automatically converts input into your variable’s datatype
f. If assigning multiple variables, use the notation:
cin >> first_variable >> second_variable >> third_variable
Your input looks like: “first_val second_val third_val” (separated by
spaces); order is important

C++ Mathematical Expressions

a. You can create complex expressions in C++
b. Expressions follow the order of operations

i. Negation first (e.g. NOT / !)
ii. Multiplication, division, modulus second (in order from left to
right)
iii. Addition/Subtraction third (in order from left to right)

c. Parentheses can override order of operations
d. For exponents, use power function pow(var, power)

Type Conversion

a. Operations can only be performed between objects of the same type
b. C++ will try to convert one type to the other, based on hierarchy of types

i. Long double (highest)
ii. Double
iii. Float
iv. Unsigned long
v. Long
vi. Unsigned int
vii. Int (lowest)

c. Type conversion can impact the result of calculations (precision!)
d. When C++ automatically converts, this is called Type Coercion; Coercion
rules:

i. Char, short, unsigned short automatically promoted to int
ii. Lower datatype gets promoted to higher datatype
iii. The result of expression will be converted to the type of the
variable the result is assigned to (e.g. if you have double var =
int foo + int blah; then int will be typecasted to type double)

e. Promotion: conversion to a higher type; Demotion: conversion to a lower
type

Overflow and Underflow

a. Occurs when value cannot fit within the bounds of the type being casted

i. Overflow occurs when value too big
ii. Underflow occurs when value too small

b. Variable is wrapped around instead, resulting in incorrect value
c. Some systems may give an error when this occurs, others continue on

Type Casting

a. Manual data type conversion (e.g. double to int)
b. Good for keeping precision when doing division with ints
c. Can use to see int value of a char (ASCII)
d. Casting expressions

i. Datatype(variable) e.g. int(foo)
ii. Static_cast<datatype>(variable) e.g. static_cast<int>(foo)

Multiple Assignment and Combined Assignment

a. Multiple assignment: Use to assign a single value to multiple variables

i. x = y = z = 5 versus x=5; y=5; z=5;
ii. Associates right to left x=(y=(z=5));

b. Combined assignment: Use to shorten your x=x*5 -type statements

i. sum+=1 instead of sum = sum+1
ii. Works with all operands +,-,*,/,%

Formatting Output

a. Used to control how numeric or string data is printed (size, position, num. of digits)

b. Use #include <iomanip> to use manipulator functions
c. Stream Manipulators: Used to control how an output field is displayed

i. See Table 3-12 on slide 43 for the various manipulators

Working with characters and string objects

a. Cin can cause problems, ignores leading whitespace
b. Use getline() to get around this issue
c. Use cin.get(variable) to read next character entered (even whitespace)
d. Don’t use cin >> and cin.get() together, can cause problems
e. Use cin.ignore() to skip characters (refer to slide 49 for params)
f. Find the length of a string with .length() (e.g. mystring.length() )
i. When using anything.method() then an object is involved
g. Join (concatenate) multiple strings together with + (string3 = string1 + string2) – can use ombined assignment operator

More Mathematical Library Functions

a. Use #include <cmath> for additional math functions

i. Trig, sqrt, log, abs val

b. Takes double as input, returns double
c. Use #include <cstdlib> for:

i. Rand() – random number generator (same sequence each time)
ii. Srand(x) – random number generator using unsigned int x (different sequence because it uses x as a “seed”)

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