Programming Chapter 3

The cin Object

• Standard input object

• requires iostream file

• Used to read input from keyboard

• Information retrieved from cin with »

• Input stored in one more more variables

• cin converts data to the type that matches the variable

• Can be used to input more than one value: cin»height»width;

• Multiple values from keyboard must be separated by spaces

• Order is important: first value entered goes to first variable

Displaying a Prompt

• A prompt is a message that instructs the user to enter data

• ALWAYS use cout to display a prompt before each cin statement

Mathematical expressions

• Can create complex expressions using multiple mathematical operators

• An expression can be literal, a variable, or a mathematical combination of constants and variables

• Can be used in assignment, cout, or another statement: area = 2*PI*radius;cout«“border is:” « 2*(l+w);

• - (unary negation) associates right to left

• *,/,%,+,- all associate right to left

• parentheses () can be used to override the order of operations

• Multiplication requires an operator: Area = l * w;

• There is no exponentiation operator: Area= pow(s,2);

• Parentheses may be need to maintain order of operations: m = (y2-y1) / (x2-X1) ;

Type Conversion

• Operations are performed between operands of the same type

  • If not of the same type, C++ will convert one to the type of the other

  • This can impact the results of the calculations

• Ranked from largest number they can hold to lowest, types are: long double, double, float, unsigned long, long, unsigned int, int

• Type Coercion: the automatic conversion of an operand to another data type

  • Promotion: Convert to a higher type

  • Demotion: Convert to a lower type

  • 1. char, short, unsigned short will automatically be promoted to int

  • 2. When operating on values of different data types, the lower one is promoted to the type of the higher one

  • 3. When using the = operator, the type of expression on the right will be converted to the type of variable on the left

• Overflow occurs when assigning a value that is too large to be held in a variable

• Underflow occurs when assigning a value that is too small to be held in a variable

• Different systems may display an error, stop the program, or continue execution using the incorrect value!!

Type Casting

• Used for manual data type conversion

• Useful for floating point division using ints

• Useful to see int value of a char variable

C-Style and Prestandard Type Cast Expressions

• C-Style cast: data type name in (): cout«ch«”is”«(int)ch;

• Prestandard C++ cast: value in (): cout«ch«”is”«int(ch);

• Both are still supported in C++, although static_cast is preferred

Multiple Assignment

• The = can be used to assign a value to multiple variables: x=y=z=5;

• Value of = is the value that is assigned

• Associates right to left (x=(y=(z=5));

Combined Assignment

• Sum = sum+1; adds one to variable sum

• Combined assignment operators provide shorthand for such statements, sum= sum+1; is equivalent to sum+=1;

• Combined assignment operators are +=, -=, *=, /=, %=

Formatting Output

• Can control how output displays for numeric, string data:

  • Size

  • Position

  • Number of digits

• Requires iomanip header file

Stream Manipulators

• Used to control how an output field is displayed

• Some affect just the next value displayed

  • setw(x): print in a field at least x spaces wide. Use more spaces is not wide enough

• Some affect values until changed again

  • fixed: use decimal notation for floating-point values

  • setprecision(x): when used with fixed, print floating-point value using x digits after the decimal. Without fixed, print floating point value using x significant digits

  • showpoint: always print decimal for floating-point values

Working with Characters and string Objects

• Using cin with the » operator to input strings can cause problems

  • It passes over ant ignores any leading whitespace characters (spaces, tabs, or line breaks)

  • To work around this problem, you can use a C++ function named getline

• To read a single character:

  • Use cin: char ch; cout « “Strike any key to continue”; cin»ch;

  • PROBLEM: Will skip over blanks, tables, <CR>

  • Use cin.get(ch);

  • Will read next character entered, even whitespace

• Mixing cin » and cin.get() in the same program can cause input errors that are hard to detect

• To skip over unneeeded characters that are still in the keyboard buffer use cin.ignore()

string Member Functions and Operators

• To find the length of a string: string state = “Texas”; in size = state.length();

• To concatenate (join) multiple strings: greeting2=greeting1 + name1;

  • Or using the += combined assignment operator: greeting1 += name2;

Basic Mathematical Library Functions

• Require cmath header file

• Take double as input, return a double

• Commonly used functions: sin, cos, tan, sqrt, log, abs

Additional Mathematical Library Functions

• Require cstdlib header file

• rand (): returns a random number (int) between 0 and the largest int the compute holds. Yields the dame sequence of numbers each time the program is run

• srand(x): initializes random number generator with unsigned int x

Uses of random numbers

Games, simulations, statistical analysis, data encryption

Generating Random Numbers

• use # include <random>

• Create a random number engine to generate a random sequence of bits and a distribution object to format the bits into numbers of a specific data type within a specified range

Hand Tracing a Program

• Acting as if you are the computer, executing a program

  • ‘Execute’ each statement one by one

  • Record the contents of variables after statement execution, using a hand trace chart (table)

• Useful to locate logic or mathematical errors