1. C++ Statements and Functions
B.Ramamurthy
CS114B
12/31/2018 BR

2. Selection Control structure
In many applications, choices are to be made depending on some conditions related to the problem. Selection or decision structures are used to model such situations. C++ supports the implementation of “selection” through the “if” and “switch” statements.
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3. Boolean expressions
Any expression (variable) that evaluates to TRUE or FALSE is a Boolean expression (variable).
example: bool Raining;
Boolean expression can be formed using logic operators (AND, OR , NOT) and/or relational operators used for comparison.
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4. Logical Operators These are also known as Boolean operators.
Operator Meaning
&& logical AND , conjunction
|| logical OR, disjunction
! negation
Example:
bool WipersOn, Dark, HeadLightsOn;
// input current conditions into WipersOn, Dark
HeadLightsOn = WipersOn || Dark;
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5. Logical expressions bool OnProbation, OutOfSchool, BackInSchool;
float GPA;
/* if OnProbation and GPA < 2.0 then OutOf School is TRUE else OutOfSchool is FALSE*/
/* if OnProbation and GPA >= 2.0 then BackInSchool is TRUE else BackInSchool is FALSE*/
OutOfSchool = OnProbation && (GPA < 2.0);
BackInSchool = OnProbation && ( GPA >= 2.0);
/*Actually OutOfSchool is the negation of BackInSchool */
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6. “if” statement Syntax: if (condition) Statements for condition True
else
Statements for condition False
Semantics:
If the condition evaluates to TRUE then execute the statements “statements for condition True”.
If the condition evaluates to FALSE then execute the statements “statements for condition False”.
After the execution of either continue on to the next statement after the “if”
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7. Multi-condition selection
Some applications require multi-level decision making and some multi-way decisions. A multi-level choice is usually implemented using nested-if and the multi-way, using the “switch” which we will discuss later.
Problem: Find the largest of a set of three distinct integers.
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8. Nested if Let the integers be N1, N2 and N3. if ( N1 > N2)
Largest = N1;
else /* ASSERT : N3 > N1 and N1 > N2 */
Largest = N3;
else /* ASSERT : N2 > N1 */
if (N2 > N3)
Largest = N2;
else /* ASSERT : N3 > N2 and N2 > N1 */
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9. Switch ... syntax switch (selector) { case label1: statements1; break;
.....
case labeln : statementsn;
default : statementsd; }
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10. switch ... semantics
Switch statement is used when there are more two alternatives to select from..
selector is an ordinal expression: That means that the values it can take should be finite, countable: integer, char, bool types are acceptable but not float.
The selector type and case label type should be same.
Each case label must be distinct.
The selector expression is evaluated and compared to each of the case labels.
If the value of the selector is one of the case labels, say label x, then the statementsx is executed.
12/31/2018 BR

11. switch ... semantics
Execution continues on until a break statement is encountered. At this point, control is transferred to the next statement after the switch.
If the selector value matches none of the labels, the default statements are executed, if one is provided. Though default provision is optional, it is a good programming practice to always have a default clause.
12/31/2018 BR

12. switch ... Example
Problem: Write a switch statement to print out the grade points corresponding to the letter grades “A”, “B” , “C”, “D”, and “F”.
switch (letter) {
case ‘A’ : points = 4.0;
break;
case ‘B’ : points = 3.0;
case ‘C’ : points = 2.0; break;
case ‘D’ : points = 1.0; break;
case ‘F’ : points = 0.0; break;
default : cout << “error in grade” << endl; }
cout << points << endl;
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13. Control structures Selection: if, if … else, switch
Selection is used to implement “mutual exclusion”; when selective execution of a piece of code is needed.
Iteration : while, for, do..while
Iteration is used when repeated execution of a piece of code is needed.
12/31/2018
B. Ramamurthy

14. Arrays An array is a collection of elements of the same type.
Good programming practice: always define a new type of the array type needed in your application.
Example: This illustrates typedef and arrays:
const int NumDays = 31;
typedef int MonthAray [NumDays];
Usage : MonthAray ThisMonth, NextMonth;
12/31/2018
B. Ramamurthy

15. Multi-dimensional arrays
typedef int arraytype [2][3]; // is this stylish? or
const int NumRow = 2;
const int NumCol = 3;
typedef int ArrayType [NumRow][NumCol]; // or is this?
Usage with initialization:
ArrayType X = {2,3,4,5};
Reference : X[1][2] = X[1][2] + X[1][1];
12/31/2018
B. Ramamurthy

16. Strings
string is a special type of array: an array of characters terminated by a null or ‘\0’
Standard library string.h provides functions that can be used with string data type.
Some of the functions: strcpy, strcmp, strcat
Strings can be input and output using the regular cin and cout respectively.
You can declare string type and variables as follows:
const int MAX_LEN = 30;
typedef char string [MAX_LEN + 1];
Usage: string Name;
12/31/2018
B. Ramamurthy

17. Structures
struct is a collection of elements not necessarily of the same type.
Good programming practice: create a new type for struct using typedef.
typedef struct PersonType { string Name;
int Age;
float GPA; };
persontype Student;
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B. Ramamurthy

18. File IO Six steps in using File IO: 1. #include <fstream.h>
2. Instantiate an object of type needed:
ifstream InFile;
ofstream OutFile;
3. Open and attach the file object with appropriate mode.
Infile.open(“Bank.dat”, ios::in);
OutFile.open(“Bank.report”, ios::out);
12/31/2018
B. Ramamurthy

19. File IO (contd.)
4. Make sure the “open” worked fine by using fail predicate function:
if (InFile.fail())
{cout<< “Error in file opening\n”;
return 1;}
5. Use the file just like you used cin and cout.
InFile >>..
OutFile << …
6. Close files when done using:
Infile.close();
OutFile.close();
12/31/2018
B. Ramamurthy

20. Input, Output using iostream
stream is a sequence of characters associated with an IO device.
ios
isa
ostream
istream
ofstream
iostream
ifstream
fstream
class hierarchy of streams.
12/31/2018
B. Ramamurthy

21. Avoiding multiple inclusion
Enclose your header files with these directives:
#ifndef unique_symbol
#define unique_symbol
header file contents
#endif
By convention, the unique_symbol is uppercase of file name inter-spaced with underscores.
12/31/2018
B. Ramamurthy

22. Function prototype, definition and call
Defines:
1) Header
2) Formal parameter names
and types
3) Statements to be executed
4) Return statement(s)
Specifies:
1) Name of
the function
2) The actual
parameters
Tells compiler:
1) function return type
2) Name of the function
3) Number of the parameters
4) Types of the parameters
5) Order of the parameters
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23. Sample Design Prototypes: void GetInput (int &, int &, int &);
: Average three integers.
MAIN
N1,N2,N3
N1,N2,N3
AVG
AVG
GetInput
Average
OutputAvg
Prototypes:
void GetInput (int &, int &, int &);
float Average (int , int, int);
void OutputAvg (int);
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24. Function prototype
Translates design into a blueprint for function definition.
Syntax:
return_type Func_name (parameter_type_list);
Where to declare a prototype? Choice 1: Outside main or in a header file.
Choice 2: For every func X called from func Y, then declare the prototype for func X inside Func Y. This truly reflects the design. Also this makes easier the transition to OOP.
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25. Parameters SampleFunc Prototype 1: int SampleFunc (int, int &);
Function header: int SampleFunc (int P1, int & P2)
====================================
Prototype 2: void SampleFunc (int, int &, int &);
Function header:
void SampleFunc (int P1, int & P2, int & P3)
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26. Types of functions Functions Library User-defined Language-defined
Examples
GetInput abs , type casting sqrt from
of Demo functions int, float math library
See Appen.B
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27. Why OO Design? Main FN1 FN2 FN3 Small Problem:
Solution: Functional decomposition
Top-down Design
Functions (Objects/Data)
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28. Why OO Design? Now consider a large problem with top-down design
as shown.
Solution: OO Design
Principle:
Identify Objects
Associate functions
Object (functions)
main
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29. From problem to OO solution
Identify the objects (“nouns”) in the problem.
Define and implement classes to represent the objects.
Class name
Data members : public, private
Function members (methods)
Service functions (usually public)
Utility functions (usually private)
Predicate functions. Example: warnings, status indicators, error indicators, etc.
Write a driver/controller that carries out the interaction among the objects.
12/31/2018
Ramamurthy

30. Summary Executable Preparation
Control structures: Selection, Repetition
Function prototype, definition and call.
Parameter passing.
Using library function.
Why Object-Oriented Design?
12/31/2018 BR