1. CPS120: Introduction to Computer Science
Basic Structure

2. Using Relational Operators
Relational operators provide the tools with which programs make decisions with true and false evaluations
== equal to NOTE: this is two equals symbols next to each other, not to be confused with the assignment operator, = > greater than < less than >= greater than or equal to <= less than or equal to != not equal to

3. Using Logical Operators
When complex decisions must be coded into an algorithm, it may be necessary to "chain together" a few relational expressions (that use relational operators)
This is done with logical operators (also called Boolean operators.)
&& is the logical AND operator || is the logical OR operator ! is the logical NOT operator

4. Complete order of operations
The complete order of operations including all of the arithmetic, relational, and logical operators including all of the basic arithmetic, relational, & logical operators is:
*, /, %
+, -
<, >, <=, >=, ==, != !
&& ||

5. Decision Making in C++ if statement switch statement
? conditional operator statement
goto statement

6. Selection Statements that include if statements and switch statements
Selection statements are sometimes called conditional or decision statements.
if (score >= 60) { cout << "I passed" << endl; } else { cout << "I'll do better next time!" << endl; }

7. Structural Review: Types of Statements
sequence
selection (if and switch structures)
iteration (for and while loops)
invocation (functions)

8. Compare and Branch
A program can instruct a computer to compare two items and do something based on a match or mismatch which, in turn, redirect the sequence of programming instructions.
There are two forms:
IF-THEN
IF-THEN-ELSE

9. IF-THEN
false
true
Entry
Exit
True statement a
Test condition p

10. Use the “IF” structure
Practically all computer languages have some sort of if structure. In C++, the if structure is a one-way selection structure:
if (number == 3) {
cout << "The value of number is 3"; }
IF structures use a control expression to determine if the code in the braces is to be executed or not

11. Compound Conditionals
You must use the AND operator (&&) to form a compound relational expression:
if (0 < number && number < 10) {
cout << number << " is greater than 0 but less than 10." << endl; }

12. IF-THEN-ELSE Entry Exit Test condition p “true” statement a
false
true
Entry
Exit
Test condition p
“true” statement a
“false” statement a

13. General Form if (test expression) { True-block statements; } else
False-block statements;
next statement;
if (c= = 'm') {
male = male + 1; }
else
fem = fem +1 ;

14. The If … Else statement
Two-way selection structure since either the block of code after the "if" part will be executed or the block of code after the "else" part will be executed but not both
The “If" part is executed if the control expression is TRUE while the "else" part is executed if the "if" part is FALSE, guaranteeing one part of the expression to be executed or the other

15. Nested If Statements
If structures and if/else statements can be nested within one another in order to model complex decision structures.
Use the braces and semicolons properly when coding such structures.

16. General Form if (test condition 1) { // true-block1 statements}
else
false-block2 statements;
false-block1 statements;
if (number % 3 == 0) {
// true-block1 statements {
cout << number << " is divisible by 3." << endl; if (number % 5 == 0) {
cout << number << " is divisible by 3 and 5." << endl; } else {
cout << number << " is divisible by 3 but not 5." << endl; }
// false-block1 statements
cout << number << " is not divisible by 3." << endl;
number++

17. Switch Structure
The switch structure is a multiple-selection structure that allows even more complicated decision statements than a two-way if/else structure allows.
It chooses one of the "cases" depending on the result of the control expression.
Only variables with the INT or CHAR data types may be used in the control expressions (i.e. parentheses) of switch statements.
Single quotes must be used around CHAR variables
Single quotes are NOT used around the integer values
Open menuOne.cpp

18. Sample Switch Structure
switch (character_entered) {
case ‘A’ :
cout << “The character entered was A.\n”;
break;
case ‘B’:
cout << “The character entered was B.\n”;
default:
cout << “Illegal entry\n”; }

19. Grouping Cases switch (number) { case 1: case 3: case 5: case 7:
cout << number << " is an even number." << endl;
break;
case 2:
case 4:
case 6:
case 8:
cout << number << " is an odd number. " << endl;
default:
cout << number << " is not a value between or including 1 and 9." << endl;
break; }

20. Iterate
A program loop is a form of iteration. A computer can be instructed to repeat instructions under certain conditions.

21. Iteration
Statements that allow the compiler to return to a point higher in the program in order to continuously repeat one or more statements
All loops including while, do/while, and for loops are prime examples of iteration statements
while (num < 10) { cout << "hello world" << endl; num = num + 1; }

22. Looping Statements Count-controlled loops
Repeat a specified number of times
Use of a special variable called a loop control variable
Flow of control of while statement

23. ‘For’ Loops
A for loop always executes a specific number of iterations.
Use a for loop when you know exactly how many times a set of statements must be repeated
A for loop is called a determinant or definite loop because the programmer knows exactly how many times it will iterate

24. Syntax of a for Loop
for (initializing expression; control expression; step expression) { // one or more statements }
The initializing expression sets the counter variable for the loop to its initial value.
The control expression ends the loop at the specified moment.
The step expression changes the counter variable
Semi-colons, not commas, divide the expressions
Example 1: Open simpFor.cpp
for (num = 1; num <= 3; num++ ) // the counter variable num is initialized to the value 1
{ // the loop will iterate while num is less than or equal to 3
cout << num; // the counter variable num increments by 1 on each iteration
cout << endl;
} // both statements are executed in the body of the loop on each iteration

25. Things to Remember About For Loops
It is possible to have variable increase by a value other than one
for (num = 1; num <= 10; num = num + 3)
It is possible to initialize the loop variable within the initializing expression. But I recommend against it
Declare loop variables at the top of the function where they belong
If an if statement only contains one body statement, the compiler doesn't require the use of curly braces

26. Looping Statements
The while statement is used to repeat a course of action
Let’s look at two distinct types of repetitions

27. Iteration Control Structures
Iteration control structures are looping mechanisms.
Loops repeat an activity until stopped. The location of the stopping mechanism determines how the loop will work:
Leading decisions
Trailing decisions

28. Leading Decisions
If the stop is at the beginning of the iteration, then the control is called a leading decision.
The command DO WHILE performs the iteration and places the stop at the beginning.

29. WHILE Loop No
Yes
Entry
Exit
Test condition p
Loop statement a

30. While Loops
A while loop does not necessarily iterate a specified number of times
As long as its control expression is true, a while loop will continue to iterate
An indeterminate or indefinite loop because only at run-time can it be determined how many times it will iterate
While is considered a top-checking loop
The control expression is located on the first line of code
If the control expression initially evaluates to FALSE, the loop will not execute even once.

31. While Loop Syntax
while (control expression) { // one or more statements }
The control expression must evaluate to TRUE in order for the while loop to iterate even once
Example2 – open whileLoop.cpp:
while (num > 100 ) // the control expression is TRUE if the variable num is greater than 100 { cout << num; num = num / 2; // the variable num is reassigned a new value during each iteration }

32. Trailing Decisions
If the stop is at the end of the iteration, the control mechanism is called a trailing decision.
The command DO UNTIL performs the iteration and puts the stop at the end of the loop.

33. DO WHILE Loop No
Yes
Entry
Test condition p
Exit
Loop statement a

34. While Loops
A while loop does not necessarily iterate a specified number of times
As long as its control expression is true, a while loop will continue to iterate
An indeterminate or indefinite loop because only at run-time can it be determined how many times it will iterate
While is considered a top-checking loop
The control expression is located on the first line of code
If the control expression initially evaluates to FALSE, the loop will not execute even once.

35. While Loop Syntax
while (control expression) { // one or more statements }
The control expression must evaluate to TRUE in order for the while loop to iterate even once
Example2 – open whileLoop.cpp:
while (num > 100 ) // the control expression is TRUE if the variable num is greater than 100 { cout << num; num = num / 2; // the variable num is reassigned a new value during each iteration }

36. Break and Continue Statements
A break statement is used to stop the execution of a loop immediately and to continue by executing the statement that comes directly after the loop
A continue statement is used to stop the execution of the statements in the loop's body on that particular iteration and to continue by starting the next iteration of the loop
Example 4: Open breakLoop.cpp
#include <iostream.h>
main() {
float num, squared; do
cout <<"Enter a number (Enter 0 to quit): ";
cin >> num;
if (num == 0)
{ break; }
squared = num* num;
cout << num << " squared is " << squared << '\n'; }
while (1);
return 0;
Example 5: Open contLoop.cpp
int i;
for (i = 1; i <= 10; i++ )
if (I == 5)
continue;
cout << i << '\n';
Return 0;

37. In Summary
Loops
goto loops -- simple if…then structure
for -- fixed number of loops
while may never be run
while (true) -- always true, needs break
do … while -- always run once
continue causes while, do… while, and for loops to start over
break causes while, do … while, for and switch statements to end

38. Invocation
Statements that allow you to place a block of statements that you wish to use several times during a program in one section
You then have the ability to "call" those statements whenever you wish to execute them without having to retype the block of statements over and over again within the program
In C++, we use "function calls" as invocation statements
displayHelloWorld( ); will call (i.e. invoke) the function below
void displayHelloWorld() { cout << "hello world" << endl; }

39. Functions

40. Function / Subprogram Statements
We can give a section of code a name and use that name as a statement in another part of the program
When the name is encountered, the processing in the other part of the program halts while the named code is executed

41. Subprogram / Function Statements
Subprogram flow of control

42. Subprogram Statements
Subprogram flow of control

43. Functions Every C++ program must have a main function
C++ may also have a number of user-defined functions
Each of the smaller tasks (let's say, subtasks) can be coded as C++ functions that go together with the to make up a structured program.

44. Library Functions
There are many functions available to C++ programmers which were written by other programmers
Use the #include compiler directive at the top of your program to take advantage of these functions.
To use the you do not even have to know exactly how they work
You do have to know how many arguments to send to the functions and what datatypes to use for those functions.

45. Function Statements
There are times when the calling unit needs to give information to the function to use in its processing
A parameter list is a list of the identifiers with which the subprogram is to work, along with the types of each identifier placed in parentheses beside the function name

46. Describing a Function
The first line of a function is called the function header
Before the name of the function you must specify a "return type."
The return type is the data type of the value that is returned by the function to the calling function
If the function does not return any value, you must type the word void as the return type
After the name of the function in the function header, you must include a parameter list.
Immediately preceding each parameter, you must identify the data type of that parameter.
Sample function header:
double computeTax(double myPrice, double myTaxRate)

47. Function Syntax
Functions are given valid identifier names, just like variables and constants.
A function name must be followed by parentheses
Coded functions are placed at the bottom of a C++ program, after the main function.
If the functions are listed after the main function, then function prototypes must be included at the top of the program, above the main function
An error will definitely result if you call a function from within the main function that has not been prototyped.
The function prototypes "warn" the compiler about the eventual use of the prototyped function and allocate memory
Example 1: A program with a function:
#include <iostream.h>
void printMyMessage(int numOfTimes); // Displays a literal a number of times
int main( ) {
int userInput = 0;
cout << "Enter a number between 1 and 10 (0 to Exit): " ;
cin >> userInput;
if (userInput != 0)
printMyMessage (userInput); }
else
cout << "Thanks, Bye!";
return 0;
} // end of main
void printMyMessage(int numOfTimes)
int i=0;
for (i=0; i<= numOfTimes; i++)
{cout << "Let's Go State!!" << endl;}
} //end of printMyMessage

48. Structure of Functions in C++
function-name(argument list) argument declaration; {  local variable declarations;  executable statement1;  executable statement2;      return (expression); }             

49. An Example of A Function
#include <iostream.h>
void printMyMessage(int numOfTimes); // PROTOTYPE and NAME
int main( ) {
int userInput = 0;
cout << "Enter a number between 1 and 10 (0 to Exit): " ;
cin >> userInput;
if (userInput != 0)
printMyMessage (userInput); // CALL STATEMENT WITH ACTUAL PARAMETER }
else
cout << "Thanks, Bye!";
return 0;
} // end of main
void printMyMessage(int numOfTimes) // FUNCTION HEADER WITH RETURN TYPE AND // ACTUAL PARAMETER
int i=0; // LOCAL VARIABLE WITHIN THE FUNCTION
for (i=0; i<= numOfTimes; i++) // BODY
{cout << "Let's Go State!!" << endl;} // OF THE
} //end of printMyMessage // FUNCTION

50. Passing Data Data is passed to functions as arguments
When a function is "called" by the main function one or more arguments are passed to the function
On the receiving end, the function accepts these arguments
The variable names of the arguments from the "calling" function do not have to be the same as the names in the "called" function.
The data types of the arguments and the parameters should match exactly

51. More About Passing Arguments
There are technically three ways to pass data as arguments to functions
passing by value is the preferred method. You simply use a variable name, an actual numeric literal, or an expression in the parentheses of the call statement
passing by reference is to be used when you want the function to actually and permanently change the values of one or more variables
You must use an ampersand (&) before the formal parameter names in the function header (the first line of the function definition) to denote passing by reference
passing by address is technically what happens when you pass an array to a function
Pass by Value Example:
#include <iostream.h> double addTax(double); int main() { double price = 10.00; double finalPrice = 0.0; finalPrice = addTax(price); cout << "The final price with tax is " << finalPrice << endl; return 0; }// end of main double addTax(double initialPrice) { return (initialPrice + initialPrice * 0.06); }// end of addTax
Passed by reference example
#include <iostream.h> void addTax(double &); int main() { double price = 10.00; addTax(price); cout << "The final price with tax is " << price << endl; return 0; }// end of main void addTax(double & incomingPrice) { incomingPrice = incomingPrice + incomingPrice * 0.06; }// end of addTax

52. Returning Values
If the function is not a void function, there must be a return statement at the end of the function
double computeTax(double myPrice, double myTaxRate) { return (myPrice * myTaxRate); }// end of computeTax
A slight modification for readability occurs if you use a local variable to first store the computed amount of tax and then return the same value as in: double computeTax(double myPrice, double myTaxRate) { double result = 0.0; result = myPrice * myTaxRate; return result; }// end of computeTax

53. Another Look at Return Values
Often, though, you want your function to return a computed value to the calling function
It is not possible in C++ to execute two return statements within a function
It is not possible to return two values in the same return statement

54. Scope of Variables
The scope of a variable is the area in which it can be legally referenced
Variables are either global or local in nature
Global variables are ones that are declared outside and above the main function
They can be used in any function throughout the program.
It is not wise to use global variables any more than you have to.
Local variables are ones that are declared inside of a function, including main. They cannot be used or referred to in other functions