POS/370

Programming Concepts Using C++

Week 3 Newsletter (E. Nikjeh)

Hello Class,

Most computer programs that solve real-world problems are much larger than the programs presented in the class and your textbook. Experience has shown that the best way to develop and maintain a large program is to construct it from smaller pieces or components each, of which is more manageable than the original program. This technique is called divide and conquer.

A function is a block of code that performs a task. Functions can greatly reduce the amount of code you need to write by creating reusable modules. Functions can create more self-documenting code, obtain more efficient code, and they can reduce maintenance costs. You can recognize a function in a program by the parentheses immediately following the function’s name. Each item of information within a function’s parentheses is called an actual argument. There are several motivations to use functions in a program. The divide-and-conquer approach makes program development more manageable. Another motivation is software reusability (using existing functions as building blocks to create new programs). A third motivation is to avoid repeating code in a program. Packaging code as a function allows the code to be executed from several locations in a program simply by calling the function.

Built-in Function:

A built-in function is a function whose task is predefined, and whose function definition (the code that guides the function in completing its task) is prewritten and appears outside of the program in which the function is used. The function definitions are contained in files, called libraries, that come with the language compiler and are available when we include a system header file (e.g. #include <math.h> and #include<string>). Examples (in class):

1- // To calculate the side of the land which is in square shape

#include<iostream.h>

#include<math.h> // We need this compiler directive to use Math. Functions

void main()

{

float side = 0.0;

float area = 0.0;

cout<<”Enter the area of your land: “<<endl;

cin>>area; //In class we entered 283024 sqft

side = sqrt(area); // sqrt is a built-in-function which is in <math.h>

cout<<”The side of the square shape of our land is “<<side<<endl;

// It prints as a result 532

}

2- // To calculate the length of a string and copy a string to a string variable

#include<iostream.h>

#include<string> // We need this to use built-in-functions for string manipulations

void main()

{

int counter = 0; //The string length

char companyName [20] = “”;// The company name with max. 20 characters

char message[] = “”;

cout<<”Enter company name: “<<endl;

cin.getline(companyName,20); //We can read space also in company name

// We entered Pacific Bell

counter = strlen(companyName);

/* the strlen is a built-in-function, which can calculate the number of characters in a string */

cout<<”The string length is “<<counter<<endl;

strcpy(message,”This is a good company”);

/* The strcpy is another built-in-function, which can copy the second argument to its first argument */

cout<<”The message is: “<<message<<endl;

// It prints The message is: This is a good company

}

3- The pow built-in-function: pow(2,5) = 32

Programmer-defined function:

The programmer can write functions to define specific tasks that could be used at many points in a program. The actual statements defining the function are written only once, and these statements are hidden from other functions. A function is invoked (i.e., made to perform its designated task) by a function call. The function call specifies the function name and provides information (as arguments) that the called function needs to do its job. A real world example is, a boss (the calling function or caller) asks a worker (the called function) to perform a task and return (i.e., report back) the results when the task is done. All variables declared in function definitions are local variables. They are known only in the function in which they are defined. Functions may or may not return information back to the calling program or function. When they don’t return information, they are known as void functions. A void function is one that returns no data to its calling function (caller). It is void (absent) of a return value. For example:

void printMenu( )

{

cout<<”*** The Data-Base Program Ver1.0***”<<endl;

cout<<”1- To add a name”<<endl;

cout<<”2- To edit a name”<<endl;

cout<<”3- To delete a name”<<endl;

cout<<”4- Quit”<<endl;

}

//This function only prints a menu and it doesn’t return a value to its caller

A function that returns a value can be used anywhere an expression can be used. For example:

monthlyPayment = calcLoan(principal,rate,term);

If(calcLoan(principal,rate,term) < = 1000.0)

monthlyPayment = monthlyPayment + 120.0;

else

monthlyPayment = monthlyPayment + 65.0;

cout<<”The monthly payment is: “<<calcLoan(principal,rate,term)<<endl;

It is a good idea to prototype our functions above the main but below the #include lines ending with a semicolon. So we inform the compiler that we will define the function later. The function header is the first line of a function that defines the return data-type, the function name, and the parameters (if there is any) without semicolon at the end. For example:

Function prototype: float calcLoan(float principal,float rate,int term);

float calcLoan(float ,float ,int );

Function header: float calcLoan(float principal,float rate,int term)

We can call the function as follows:

monthlyPayment = calcLoan(principal,rate,term);

In the function header we can have different variable names like:

float calcLoan(float loanAmount, float interestRate, int years)

{

-----

}

We call the variable loanAmount, interestRate, and years dummy variables.

Here we pass the variables to the function by value (the value of principal to loanAmount, the value of rate to interestRate, and the value of term to years). This way of passing variables is called call by value. The computer passes only the contents of the variable to the receiving function. The receiving function is not given access to the variable in memory, so it cannot change the value stored inside the variable. Passing a variable’s address instead its value is called call by reference. It gives the receiving function access to the variable being passed. So the receiving function can change the contents of the variable (like the program example in the class). To pass a variable by reference to a function, we include an ampersand (&) before the name of the corresponding formal parameter in the function header. We also must include the & in the function prototype after the data type. For example:

In function prototype: float calcLoan(float &principal,float rate,int term);

float calcLoan(float &, float , int );

In function header: float calcLoan(float &principal,float rate,int term)

The variable principal is called by reference and variables rate and term are called by value.

Global Variable:

If we declare a variable with its data type above the main, we can use it in entire of our program even in any function without declaring it again and we can change its value anywhere.

Selection (decision) Structure:

When we want a program to make a decision or comparison and then, based on the result of that decision or comparison, select one of two paths. Most programming languages offer three forms of the selection structure: if, if/else, and switch (also called case). We have different types of if statements as follows:

1- if (condition) one statement; /* if condition is true, it executes the statement and goes to the statement below if otherwise it goes to the statement below if */

2- if (condition) { multiple statements require braces}/* if condition is true it will execute the statements inside the braces and then goes to the statement below the if */

3- if (condition) one statement;

else

one statement;

4- if (condition) {one or more statements}

else

{one or more statements}

5- Nested if:

if (condition1) {one or more statements}

else

if (condition2) {one or more statements}

else

if(condition3) {one or more statements}

else

. . .

if (condition N) {one or more statements}

else {one or more statements}

The condition portion of the if statement can contain a single statement or several compound expressions connected with logical operators, but it can only yield a true or false answer. Try to avoid nesting more than five levels.

Comparison (relational) operators:

operator operation Precedence number

< <= less than, less than or equal to 1

> >= greater than, greater than or equal to 1

= = equal to 2

!= not equal to 2

Switch Statement: The switch statement allows for multiple paths with default, but it can only compare the value of an int, short, long, or char data-type. Each path is specified using the case keyword followed by one or more statements ending with break statement. The break would cause the switch to exit. For example:

Switch (gradeLetter)

{

case(‘A’): cout<<”Excellent”<<endl;

break;

case(‘B’): cout<<”very good”<<endl;

break;

case(‘C’): cout<<”Good”<<endl;

break;

case(‘D’): cout<<”Pass”<<endl;

break;

case(‘F’): cout<<”Please take the course again”<<endl;

break;

default: cout<<”Wrong letter grade entered”<<endl;

break;

} //The switch multiple-selection structure with breaks

Four program examples in the class: Example 1-

/* This program reads a string with a space and prints it. It also uses the string built in functions to calculate the string length and to copy a string to a string variable. It also calculates the side of a square land that we have its area by using math built in function */

#include<iostream.h>

#include<string>

#include<math.h>

void main( )

{

float area = 0.0;

float side = 0.0;

char message[] = ""; // This is array of characters (string) with any number of characters

char coName[] = "";

int counter = 0;

cout<<"Enter the company name"<<endl;

cin.getline(coName,20 );//We can read the company name(max 20 characters) with space

cout<<"The company name is "<<coName<<endl;

counter = strlen(coName);// strlen(built in function) calculates string length of a string

cout<<"The number of the string is "<<counter<<endl;

strcpy(message,"This is a good company");// strcpy copies the second string to the first

cout<<message<<endl;

cout<<"Enter the area of your land: "<<endl;

cin>>area;

side = sqrt(area);// sqrt is built in function to calculate square root of a number

cout<<"the side is "<<side<<endl;

}

// This program calculates the monthly payment of your loan

#include<iostream.h>

#include<math.h>

void main( )

{

double payment = 0.0;// monthly payment

double principal = 0.0;// loan amount

double rate = 0.0;// interest rate

int term = 30;// the loan term which is 30 years

cout<<"Enter your loan principal: \n";

cin>>principal;

cout<<"Enter the loan interest rate: "<<endl;

cin>>rate;

rate = rate/(double)12.0;// to find the rate for one month

term = term*12;// to find the term in months

payment = principal*rate / (1.0 - pow(rate + 1.0, -(double)term));// formula to calculate

cout<<"Your monthly payment is $"<<payment<<endl;

}

// This program calculates monthly payment for your loan using function (call by value)

#include <iostream.h>

#include <math.h>

#include<iomanip.h>

// This is a function prototype

double loanCalc(double principal,double rate);

int term = 30; // term is a global variable

void main()

{

double principal = 0.0;

double payment = 0.0;

double rate = 0.0;

double totalPayments = 0.0;

cout<<"Enter the principal: "<<endl;

cin>>principal;

cout<<"Enter the annual interest rate: "<<endl;

cin>>rate;

payment = loanCalc(principal,rate);// It calls the function loanCalc

cout<<"The payment is $"<<payment<<endl;

totalPayments = 360.0 * payment;

cout<<setiosflags(ios::fixed);// displys in fixed point notation

cout<<"your total payments after 30 years is $"<<totalPayments<<endl;

}

// This function calculates the monthly payment

// program-defined function

double loanCalc(double principal,double rate)

{

double mpayment =0.0;// local variable

rate = rate/(double)12.0;

term = term*12;

mpayment = principal*rate/(1.0 - pow(rate+1.0,-(double)term));

cout<<"Your monthly payment is $"<<setprecision(5)<<mpayment<<endl;

cout<<"Your term is "<<setw(10)<<term/12<<" years fixed."<<endl;

return mpayment;

}

// This program calculates the monthly payment of your loan using function (call by reference)

#include<iostream.h>

#include<math.h>

#include<iomanip.h>

// The user-defined function to calculate the payment

double calcLoan(double &,double );// Function prototype to calculate the monthly payment

void title( ); /* Function prototype-It prints the title of the program. It is void because it doesn’t return any value */

// term is global variable and we can use it without declaration in the entire program

int term = 0;

void main( )

{

double payment = 0.0;//monthly payment

double principal = 0.0;// loan amount

double rate = 0.0;// interest rate

title( );// it calls the function to print the title

cout<<"Enter your loan principal: \n";

cin>>principal;

cout<<"Enter the loan interest rate: "<<endl;

cin>>rate;

cout<<"Enter the term of your loan: "<<endl;

cin>>term;

payment = calcLoan(principal,rate);

cout<<"Your monthly payment is $"<<payment<<endl;

cout<<setiosflags(ios::fixed); //We can have fixed point instead floating point

// setprecision(2) is a built in function. It shows two digits after decimal point

cout<<"The pricipal is $"<<setprecision(2)<<principal<<endl;

}

// This function calculates the monthly payment and returns a value

double calcLoan(double &loanAmount,double intRate) // call by reference loanAmount

{

double mPayment = 0.0;

rate = rate/(double)12.0;

term = term*12;

mPayment = loanAmount*intRate / (1.0 - pow(intRate + 1.0, -(double)term));

loanAmount = loanAmount*2;

return mPayment;

}

// This function prints the title and it doesn’t return any value so it is void

void title( )

{

cout<<" *** The calculation for loan process ***"<<endl;

}

// To read a grade and to print the grade letter

#include <iostream.h>

void main()

{

float grade = 0.0;

char gletter = ' ';

cout<<"Enter your grade: "<<endl;

cin>>grade;

if(grade > 100.0) cout<<"Wrong grade entry"<<endl;

else

if(grade >= 90.0)

{

cout<<"Your grade letter is A"<<endl;

gletter = 'A';

}

else

if(grade >= 80.0)

{

cout<<"Your grade letter is B"<<endl;

gletter = 'B';

}

else

if(grade >= 70.0)

{

cout<<"Your grade letter is C"<<endl;

gletter = 'C';

}

else

if(grade >= 60.0)

{

cout<<"Your grade letter is D"<<endl;

gletter = 'D';

}

else

{

cout<<"Your grade letter is F \n You are failed\n";

gletter = 'F';

}

switch (gletter)

{

case('A'): cout<<"Excellent"<<endl;

break;

case('B'): cout<<"Very good"<<endl;

break;

case('C'): cout<<"Good"<<endl;

break;

case('D'): cout<<"Bad"<<endl;

break;

case('F'): cout<<"Please take the course again"<<endl;

break;

default: cout<<"Wrong letter grade entered"<<endl;

cout<<"Please enter grade letter again"<<endl;

break;

}

It is a good programming practice if you run these programs again.

Have a nice day.

See you in class

Esmaail M Nikjeh