Class 2: Variables and Memory. Laura Marik Spring 2012 C++ Course Notes (Provided by Jason Minski)

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1 Class 2: Variables and Memory

2 Variables A variable is a value that is stored in memory It can be numeric or a character C++ needs to be told what type it is before it can store it in memory It also needs a name the identifier so that it can be referred to

3 Numeric Types int num_apples = 3; double pi = ; A numeric type can be either an integer type (int) or a floating point type (double). There are other integer and floating point types, but int and double are the most commonly used.

4 Declaration of Variables Syntax: Examples type identifier; type identifier = value; type identifier1, identifier2, etc. int grade1; int grade2 = 93; int grade3 = 92, grade4, grade5 = 71;

5 What the declaration does Tells the computer what kind of variable you are creating It gets placed at the bottom of the memory stack

6 Identifiers Identifiers must be composed of letters, digits and underscores. They cannot begin with a digit They cannot be reserved words in C++ Style: Identifiers should be meaningful, self-documenting Example: int abcde int 1abcde int abcde1 int abc_de int abc-de int double; valid invalid valid valid invalid invalid

7 Example A program is to calculate the wind chill for a temperature of 72.5 F and a wind speed of 20 mph. The formula for wind chill is as follows (where T is the temperature and V is the wind speed): T 35.75V TV 0.16

8 Windchill Program

9 Observations 1. The values for wind speed and temperature are hard coded in the program. It would be an improvement if they could be entered by the user. 2. C++ has libraries of useful functions like pow. The header file which declares the function must be #included at the top of the program. 3. To display the value of a variable to the screen, use cout << variablename << endl

10 Standard Input and Output int num_trees; cout << enter number of trees << endl; cin >> num_trees; cout << The user has entered << num_trees << endl;

11 Windchill program: data taken from user

12 The assignment operator (=): changing the value of a variable In math, we use = in two ways as an action: let n = 2 as a claim: if n = 3, then... In C++, there are two different operators for this Assignment: n = 2; Equality: if ( n == 3 )

13 Example: what happens on the memory stack int i = 1; int j; j = i; i = 2*j; j = i + 1; i = 3*i;

14 Floating point versus integer arithmetic Mod operator: i % j = the remainder of i when divided by j they must be integer types Ex: 17%2 1 Division operator: i/j gives the value of i divided by j if both are integer types, the result is an integer, which the fractional part truncated if either is a floating point type, the result is also a floating point number Ex: 17/ / / /

15 Example Write a program that gets a 5 digit number from the user. If the number is not a 5 digit number, it exits with a message telling the user. If it is a 5 digit number, it displays the sum of all the digits. New C++ needed: if (A B) { } else { } exit(-1); a conditional statement, means or exit the program, -1 indicates an error has occurred.

16 Type casting a double can be cast to an int, or an int to a double Examples: int(2.5) 2 double(2) 2.0 2/5 0 double(2)/ int(2.5) 0.5

17 Assignment #1 a. Write a program that gets the month (as a value between 1 and 12) and the day of the month from the user for two dates (in the same year). If the month or day is not valid, it gives a message to the user and exits. Otherwise, it displays a message, either that both dates are the same day of the week, or that they are different days of the week. Your program should work for non leap years.

Review: Exam 1. Your First C++ Program. Declaration Statements. Tells the compiler. Examples of declaration statements

Review: Exam 1. Your First C++ Program. Declaration Statements. Tells the compiler. Examples of declaration statements Review: Exam 1 9/20/06 CS150 Introduction to Computer Science 1 1 Your First C++ Program 1 //*********************************************************** 2 // File name: hello.cpp 3 // Author: Shereen Khoja