1. Chapter 2 Assignment and Interactive Input
Program Development and Design Using C++, Third Edition

2. Program Development and Design Using C++, Third Edition
Objectives
You should be able to describe:
Assignment Operations
Interactive Keyboard Input
Program Development and Design Using C++, Third Edition

3. Assignment Operations
Most basic statements for assigning values to variables and performing computations
variable = expression;
Equal sign tells computer first to:
Determine value of operand to right
Store (assign) value in location(s) associated with the variable to left
Expression: Combination of constants, variables, and function calls that can be evaluated to a result
e.g. The assignment statement:
total=30; is valid.
total+10=30; is NOT valid.
Program Development and Design Using C++, Third Edition

4. Assignment Operations (continued)
Assignment operator: The = symbol
Lower precedence than any other arithmetic operator
Assignment expression: Expression using assignment operator
Has a value
Multiple assignments possible in same expression
Assignment operator has right-to-left associativity
Program Development and Design Using C++, Third Edition

5. Program Development and Design Using C++, Third Edition
Coercion
Data type conversions take place across assignment operators
Coercion: Value assigned to variable on left of assignment operator forced into data type of variable it is assigned to
Integer value assigned to real variable
Real value assigned to integer variable
Pay attention to mixed-mode expressions
Program Development and Design Using C++, Third Edition

6. Assignment Variations
Variable to left of equal sign can also be used on the right of equal sign
e.g., sum = sum + 10;
Remember operator precedence
Shortcut assignment operators: += -= *= /= %=
Program Development and Design Using C++, Third Edition

7. Assignment Variations (continued)
Figure 3.4: sum = sum + 10; Causes a New Value to Be Stored in sum
Program Development and Design Using C++, Third Edition

8. Accumulating Program 3.3: Accumulating Example
Program Development and Design Using C++, Third Edition

9. Program Development and Design Using C++, Third Edition
Counting
Counting statements have form:
variable = variable + fixedNumber;
Increment operator: ++
variable++ equivalent to variable = variable + 1
Prefix increment operator: ++variable
Increment, then use variable
Postfix increment operator: variable++
Use variable, then increment
Program Development and Design Using C++, Third Edition

10. Program Development and Design Using C++, Third Edition
Counting (continued)
Decrement operator: --
Variable-- equivalent to variable = variable - 1
Prefix decrement operator: --variable
Decrement, then use variable
Postfix decrement operator: variable--
Use variable, then decrement
Program Development and Design Using C++, Third Edition

11. Interactive Keyboard Input
Programs that do same calculation on same set of numbers every time not very useful
cin object: Used to enter data into program while executing
(“get from”) operator, >>
Prompt: String telling person at terminal what should be typed
cin object puts computer into temporary pause state until user types a value
Program Development and Design Using C++, Third Edition

12. Interactive Keyboard Input (continued)
Figure 3.10: cin Is Used to Enter Data; cout Is Used to Display Data
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13. Interactive Keyboard Input (continued)
Any number of values can be input using single cin statement
cin extraction operation able to make some data type conversions
Program Development and Design Using C++, Third Edition

14. Program Development and Design Using C++, Third Edition
Example 1
#include <iostream>
using namespace std;
int main() {
double num1, num2, product;
cout << "Please type in a number: ";
cin >> num1;
cout << "Please type in another number: ";
cin >> num2;
product = num1 * num2;
cout << num1 << " times " << num2 << " is " << product << endl;
return 0; }
Program Development and Design Using C++, Third Edition

15. Program Development and Design Using C++, Third Edition
Example 2
#include <iostream>
using namespace std;
int main() {
int num1, num2, num3;
double average;
cout << "Enter three integer numbers: ";
cin >> num1 >> num2 >> num3;
average = (num1 + num2 + num3) / 3.0;
cout << "The average of the numbers is " << average << endl;
return 0; }
Program Development and Design Using C++, Third Edition

16. Interactive Keyboard Input (continued)
Figure 3.11: Inputting Data into Variables num1, num2, and num3
Program Development and Design Using C++, Third Edition

17. A Closer Look: Programming Errors
An error can be detected:
Before program is compiled
While program is being compiled
While program is being run
After program has been executed and output is being examined
Program Development and Design Using C++, Third Edition

18. A Closer Look: Programming Errors (continued)
Compile-time errors: Errors detected by compiler
Syntax errors and parse errors
Run-time errors: Errors that occur while program is running
Logic errors
Ways to protect against run-time errors:
Anticipate what user might do to cause errors
Rigorous testing
Program Development and Design Using C++, Third Edition

19. A Closer Look: Programming Errors (continued)
Desk checking: Checking program code for syntax and logic errors
Program testing: Detecting errors during or after program execution
Logic errors never caught by compiler
Plan program testing carefully
Maximize possibility of locating errors
Program Development and Design Using C++, Third Edition

20. A Closer Look: Programming Errors (continued)
Bug: Program error
Debugging: Process of isolating errors, correcting them, and verifying corrections
Program tracing: Imitate computer and execute statements by hand
Echo printing: Add temporary code to display values of input data
Debugger: Controls execution of program
Can interrupt program at any point
Can display values of all variables
Program Development and Design Using C++, Third Edition

21. Exercise: Find the errors
#include <iostream>
using namespace std;
int main() {
width = 15
area = length * width; cout << “The area is “ << area }
Program Development and Design Using C++, Third Edition

22. Program Development and Design Using C++, Third Edition
Reading and Homework
Reading:
Chapter 2: pg.83-end of chapter.
Chapter 3: pg and pg
Homework:
Pg. 110: ex.1, 2, 6, and 9.
Pg : ex. 2, 4a, 5.
Program Development and Design Using C++, Third Edition