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Week 2.1 Numerical Data Types and Variables.pdf

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Chapter 2: Numerical Data

Types & Variables to Represent

Them

CSE 2010: Week 2

What this lecture

covers:

  • Data types
    • What they are.
    • The data types used to represent numerical values.
  • Variables
    • What they are
    • Declaring and Initializing them
    • Using them in your programs
    • Assigning them new values

Data Types:

Background and Definition

  • Background: When we are writing a program, we have to represent different types of values depending on the task at hand. C++ is able to represent simple numerical and character values using specific, fundamental data types.
  • Definition: Values in programming have a specific data type that determines the size it will take up in memory, and the type of value that can be stored at that memory location.

Data Types:

Integer and Floating-Point

  • Numeric data:
    • Integers and floating point aka decimal numbers.
  • Integer values:
    • Whole #’s with no fractional part (negatives, zero, positives).
  • Floating-Point values:
    • Numbers with decimal points in them. “Floating-point” refers to the decimal floating around and changing the value of the number.
C++
Keyword
Size of type (memory
allocated)
Range of values that can
be stored in this type
int 4 bytes -2,147,483,648 to
2,147,483,

C++
Keyword

Size of type (memory
allocated)

Range of values that can be
stored in this type
float 4 bytes ±1.18 x 10-38to ±3.4 x 10^38
double 8 bytes ±2.23x 10-308to ±1.80 x 10^308

Number Types:

(Big C++, 2ndEdition, pg. 39, Table 1)

Variables:

Background & Definition

  • Background:
    • When writing a program to complete a specific task, it is very likely we must save values throughout the program to use them later. We need a way to store these values in memory and use them whenever we need to.
  • Definition:
    • Variables are named storage that can be used throughout a program. They allow us to store values in memory and access them later without having to note the physical address in memory.

Variables:

C++ Syntax for variable declaration/definition

  • datatype variableName;
    • Declares a single variable with no initial value
    • Example:int x1;
  • datatype variableName, variableName, variableName...;
    • Declares multiple variables of the same datatype, all with no initial values. Separate each variable name with a comma.
    • Example:int x, y, z;
  • datatype variableName = initial value;
    • Defines a single variable with an initial value
    • Example:int age = 30;
  • datatype variableName = initial value, variableName = initial value...;
    • Defines multiple variables of the same datatype, each with their own initial values
    • Example:double price1 = 30.99, price2 = 41.55, price3 = 25.25;
  • Notes:
    • You can declare/define as many variables as you want in a single statement, but they all must be the same data type.
    • The “=” character used above is the assignment operator.
    • Format is: variable = value; Where it will assign the variable on the left the value on the right.

Variables:

Rules for Variable Names

  • Variable names must start with a letter or , but can then contain a mix of uppercase & lowercase letters, numbers, and . (No other non-letter characters allowed)
  • Cannot be any C++ keywords (int, float, double, main, class, case, pg. 960 in textbook)
  • Variable names are case sensitive, so the variables: int pennies; int Pennies; // would be seen as different variables
  • Make variable names something significant. It should be clear what the variable represents.

Variables: Integer Values

  • C++ keyword : int
  • When to use int
    • Use intto represent data that can only be identified in whole numbers
    • age, number of coins, ID numbers, the year, int age; int pennies; int coyoteID; int year;
  • Can perform arithmetic with integers ( +, -, *, /, % ) int x = 30, y = 6, z =7; int b = x + y; // b = 36 int s = x – y; // s = 24 int t = x * y; // t = 180 int u = x / y; // u = 5 int v = x / z; // v = 4 (Integer Division)
  • Modulus Operator: %
    • op1 % op2 results in the remainder of dividing op1 by op
    • Example: int x = 30, y = 6, z =7; int v = x % y; //v = 0 int w = x % z; // w = 2

Variables:

Assigning new values to variables

  • Variables are called variables for a reason...their values can change!
  • Syntax: variableName = value;
    • This value can be any expression that is the same data type as the variable
      • Constant value
      • Arithmetic expression
      • Function call
      • Combination of everything Example: int x = 60, y = 10; x = x + y; // x = 70 x = 100 + y; // x = 110
  • You can combine the assignment operator with an arithmetic operator to assign a new value int count = 0; count = count + 1; //count = 1OR int count = 0; count +=1; // count = 1
  • a op= b a = a op b can be used with -=, *=, /=, %=

Variables:

Incrementing and Decrementing with Unary Operators

  • Increment and decrement operators
  • ++ increment by 1
  • -- decrement by 1
  • pre-increment/pre decrement (++x,--x): increment/decrement x by 1, and THEN access value
  • post increment/post decrement (x++, x--) : access the value of x, and THEN increment/decrement by 1
  • Examples: int x = 6; int z = x++ * 3; // After the above two statements, z = 18 and x = 7 int y = 3; int t = ++y * 5; // After the above two statements, t = 20, and y = 4

Variables:

Floating-Point Values

C++ keyword : double
  • When to use double
    • Use doublewhen the value with contain decimal points
    • Monetary ($$) values, physics problems, math problems double speed; double price; double pi; double volume;
  • Similarly, to integers, we can use arithmetic operators on these types ( +, -, *, /, % ) double length = 9.5; double width = 10.6; double area = length * width; //area = 100. double x = 5/2; //2.
  • Note:
    • Cannot use % with floating point values.
    • Can use fmod(),part of the cmath library

Variables: Constants

  • Constants:
    • A constant is a named value that cannot be changed.
    • Use constants in your program when you are representing a fixed value.
  • Syntax: const datatype NAME = value;
  • Example: const double PI = 3.1415926535; double radius = 0; cout << “Enter the radius of the circle: “; cin >> radius; cout << “The area of the circle is: “ << PI * r * r << “\n”;

Let’s come up with the steps to solve the following problem

  • Steps to take • What we need for each step:

Write a C++ program that asks the user the number of pennies, nickels, dimes, and quarters they have. Then, display their total to them.