Introduction to C++

History

• It was developed by Bjarne Stroustrup in Bell Labs, 1979
• It is an extension of the C language
  • It has a number of features compared to older programming language
    • Such features are object-oriented programming, generic programming, and exception handling
• It became one of the most popular programming languages.

Structure

• Core Language:

  • foundation of C++
  • includes all essential features of languages:
    • data types
    • classes
    • variables
    • functions

• Standard Library

  • provides a wide range of functions and classes already embedded in the language
    • some examples are:
      • input/output
      • string manipulation
      • math operations

• Third-party Libraries

  • provides additional functionalities to C++ not included in the language itself
  • some examples include game development, scientific computing, and machine learning.

• Preprocessor Directives

  • used to control the preprocessor.
    • a program that runs before the compiler
    • can be used to include header files, macros, and conditionally compile code.

• Global Declaration

  • defines variables, functions, or classes accessible to all parts of the program

• Function Definition

  • defines a code that is executed when a function is called

• Main Function

  • the entry point for all C++ programs
  • the first function to be called when the program is executed.

• Below is an example of C++ program.

intro.cpp

#include <iostream>
using namespace std;
int main() {
	int a, b, c;
	cout << "Enter two numbers: ";
	cin >> a >> b;
	c = a + b;
	cout << "The sum of " << a << " and " << b << " is " << c << endl;
	return 0
}

• Each line or set of instruction we use inside a program is called a statement.

Converting Flowcharts into C++ Code

Suppose that we have the following sequential flowchart below:

flowchart TD
	start(["Start"])
	init{{"a = 0\nb = 0\nsum = 0"}}
	input[\"Input a, b"\]
	process["sum = a + b"]
	output[\"Output sum"\]
	stop(["End"])
	
	start --> init
	init --> input
	input --> process
	process --> output
	output --> stop

This flowchart shows us that by inputting two numbers a and b, we output its resulting sum.

But, how can we turn this into working C++ code?

We do this by writing our code based on how our flowchart is organized.


Step 1: Start the code by writing our necessary syntax.

flowchart TD
	start(["Start"])

• Here, we often introduce header files, namespaces, and even the main function itself.
• Take note that there are some differences when writing code for Turbo C++ and some modern compilers.

Modern C++

#include <iostream>
using namespace std;
 
int main () {
	
}

• Depending on the compiler we use, there may be some changes with the syntax we use to start our code.

Step 2: Initialize the variables.

flowchart TD
init{{"a = 0\nb = 0\nsum = 0"}}

• To initialize our variables, we declare a variable inside the main function definition.
  • We simply write int then followed by our variable, for example, a, then the initial value for that variable.
  • We simply follow what our flowchart says and we set the initial value for each variable as 0.
  • Remember, that as we put an another statement inside main, we end each statement with a semicolon ;

Modern C++

#include <iostream>
using namespace std;
 
int main () {
	int a = 0;
	int b = 0;
	int sum = 0;
}

Tip
Declaring Multiple Variables

When we declare multiple variables such as in this case, we can instead simplify them into a single statement.

int main () {
	int a = 0, b = 0, sum = 0;
}

Here, each variable assignment is separated by a comma.
We can do this to make our code more compact.

Step 3: Use cout and cin for user input/output.

flowchart TD
input[\"Input a, b"\]

• The next thing in our flowchart is to input numbers to our code.
• First, we let the user know that we need to input a value.
  • We do this by writing cout << "Enter the first number: ";.
    • cout means to display something to the user, as in for output.
    • When we want to use actual text in our code, we enclose them in double quotes "".

Modern C++

#include <iostream>
using namespace std;
 
int main () {
	int a = 0, b = 0, sum = 0;
	cout << "Enter the first number: ";
}

• Now that the user knows that we need to input something, we now use cin >> a.
  • This allows us to assign a value to a variable to our first number a.

Modern C++

#include <iostream>
using namespace std;
 
int main () {
	int a = 0, b = 0, sum = 0;
	cout << "Enter the first number: ";
	cin >> a;
}

• We then do the exact same thing, this time for the second number b.

Modern C++

#include <iostream>
using namespace std
 
int main () {
	int a = 0, b = 0, sum = 0;
	cout << "Enter the first number: ";
	cin >> a;
	cout << "Enter the second number: ";
	cin >> b;
}

Step 4: Perform the necessary operations.

flowchart TD
	process["sum = a + b"]

• In this step, we perform the operations that we need.
• In this case, we are asked to add a and b, then we assign its value to the variable sum.

Modern C++

#include <iostream>
using namespace std;
 
int main () {
	int a = 0, b = 0, sum = 0;
	cout << "Enter the first number: ";
	cin >> a;
	cout << "Enter the second number: ";
	cin >> b;
	sum = a + b;
}

Step 5: Output the resulting value.

flowchart TD
	output[\"Output sum"\]

• Now, what we want to do is to output the sum.
  • We do this by using the cout command again, then output the contents of the variable sum.

Modern C++

#include <iostream>
using namespace std;
 
int main () {
	int a = 0, b = 0, sum = 0;
	cout << "Enter the first number: ";
	cin >> a;
	cout << "Enter the second number: ";
	cin >> b;
	sum = a + b;
	cout << sum;
}

Step 6: Terminating the code.

flowchart TD
stop(["End"])

• To end our code, we add that statement return 0; to tell the compiler that this is the end of our code.

Modern C++

#include <iostream>
using namespace std;
 
int main () {
	int a = 0, b = 0, sum = 0;
	cout << "Enter the first number: ";
	cin >> a;
	cout << "Enter the second number: ";
	cin >> b;
	sum = a + b;
	cout << sum;
	return 0;
}

Finetuning

We can also use some information that may allow us to clean our code!

• Detailed Outputs
  • Aside from simply displaying the sum, we can add more information by explicitly letting the user know that the resulting value is a sum.
  • We can do this by writing them like text then we join them with <<
    - For example, the statement cout << "The sum of " << a << " and " << b << " is " << sum; will give us The sum of a and b is sum replacing whatever a or b or their sum sum be.

sum-detail.cpp

#include <iostream>
using namespace std;
 
int main () {
    int a = 0, b = 0, sum = 0;
    cout << "Enter the first number: ";
    cin >> a;
    cout << "Enter the second number: ";
    cin >> b;
    sum = a + b;
    cout << "The sum of " << a << " and " << b << " is " << sum;
    return 0;
}

• Newlines:
  • A newline simply says that we are telling the computer that we want to output this section in the next line in the terminal.
  • For instance, we went to insert a newline between the outputs Enter the second number: and The sum of ...
    • We would instead put \n before "The sum of ..." in line 11.

sum-detail.cpp

#include <iostream>
using namespace std;
 
int main () {
    int a = 0, b = 0, sum = 0;
    cout << "Enter the first number: ";
    cin >> a;
    cout << "Enter the second number: ";
    cin >> b;
    sum = a + b;
    cout << "\nThe sum of " << a << " and " << b << " is " << sum;
    return 0;
}

• endl manipulators
  • Speaking of newlines, we use endl to add a newline at the end of an output.
  • We usually do this so that the outputs get more organized.
    • To show this, we modify the code to output the average of the average of the two numbers as well.

avg-no-endl.cpp

#include <iostream>
using namespace std;
 
int main () {
    int a = 0, b = 0, sum = 0, avg = 0;
    cout << "Enter the first number: ";
    cin >> a;
    cout << "Enter the second number: ";
    cin >> b;
    sum = a + b;
    avg = sum / 2;
    cout << "\nThe sum of " << a << " and " << b << " is " << sum;
    cout << "\nThe average of " << a << " and " << b << " is " << avg;
    return 0;
}

avg-with-endl.cpp

#include <iostream>
using namespace std;
 
int main () {
    int a = 0, b = 0, sum = 0, avg = 0;
    cout << "Enter the first number: ";
    cin >> a;
    cout << "Enter the second number: ";
    cin >> b;
    sum = a + b;
    avg = sum / 2;
    cout << "\nThe sum of " << a << " and " << b << " is " << sum << endl;
    cout << "\nThe average of " << a << " and " << b << " is " << avg;
    return 0;
}

Exercises

Convert the following flowcharts and programs into executable C++ code.

1. Input two numbers n1 and n2.
   Display the sum, difference, product, and the quotient of the two numbers.

flowchart TB
	start(["Start"])
	init{{"n1 = 0\nn2 = 0\nsum = 0\ndiff = 0\nprod = 0\nquot = 0\n\n"}}
	input[/"Input n1, n2"/]
	process["sum = n1 + n2\ndiff = n1 - n2\nprod = n1 * n2\nquot = n1 / n2\n\n"]
	output[/"Output sum, diff, prod, quot"/]
	stop(["End"])
	
	start --> init
	init --> input
	input --> process
	process --> output
	output --> stop

Solution

operations.cpp

include <iostream>
using namespace std;
 
int  main () {
int n1 = 0, n2 = 0, sum = 0, diff = 0, prod = 0, quot = 0; // Initialization
cout << "Enter the first number: "; // Lets user know to input number 
cin >> n1;
cout << "Enter the second number: ";
cin >> n2;
 
// Calculates sum, difference, product, and quotient
sum = n1 + n2;
diff = n1 - n2;
prod = n1 * n2;
quot = n1 / n2;
 
//Outputs them with human language
cout << "The sum of " << n1 << " and " << n2 << " is " << sum << endl;
cout << "The difference of " << n1 << " and " << n2 << " is " << diff << endl;
cout << "The product of " << n1 << " and " << n2 << " is " << prod << endl;
cout << "The quotiont of " << n1 << " and " << n2 << " is " << quot << endl; 
return 0;
}

2. Input the length and height of the rectangle.
   Display its area and perimeter.

flowchart TB
	start(["Start"])
	init{{"length = 0\nwidth = 0\narea = 0\nperimeter = 0\n\n"}}
	input[/"Input length, width"/]
	process["area = length * width\nperimeter = 2 * (length + width)"]
	output[/"Output area, perimeter"/]
	stop(["End"])
	
	start --> init
	init --> input
	input --> process
	process --> output
	output --> stop

Solution

rectangle.cpp

#include <iostream>
using namespace std;
 
int main () {
  int length = 0, width = 0, area = 0, perimeter = 0;
  cout << "Enter the length of the rectangle";
cin >> length;
  cout << "Enter the width of the rectangle";
  cin >> width;
  
  area = length * width;
  perimeter = 2 * (length + width);
  
  cout << "The area of a " << length << " by " << width << " rectangle is " << area << endl;
  cout << "The perimeter of a " << length << " by " << width << " rectangle is " << perimeter << endl;
  return 0;
}

3. Input the radius of a circle.
   Display its diameter, area, and circumference.

flowchart TB
	start(["Start"])
	init{{"radius = 0\ndiameter = 0\narea = 0\ncircumference = 0\n\n"}}
	input[/"Input radius"/]
	process["diameter = 2 * radius\narea = 3.14159 * radius * radius\nperimeter = 3.14159 * diameter"]
	output[/"Output area, circumference, diameter"/]
	stop(["End"])
	
	start --> init
	init --> input
	input --> process
	process --> output
	output --> stop

Solution

circle.cpp

#include <iostream>
using namespace std;
 
int main () {
  int radius = 0, diameter = 0, circumference = 0, area = 0;
  cout << "Please enter the radius of the circle: ";
  cin >> radius;
  
  diameter = radius * 2;
  circumference = 3.14159 * diameter;
  area = 3.14159 * radius * radius;
  
  cout << "The diameter of a circle with radius " << radius << "is " << diameter << endl;
  cout << "The circumference of a circle with radius " << radius << "is " << circumference << endl;
  cout << "The area of a circle with radius " << radius << "is " << area << endl;
  return 0;
}

4. (From ComProg Q1 Activity (09-19-24)) modified
   Input the employee number, rate per hour, and the number of hours worked. Compute and display the basic salary by multiplying the rate per hour and number of hours worked. Compute and display also the SSS deduction which is 20% of the basic salary, PAG-IBIG deduction amounting to 200 pesos, PhilHealth deduction which is 5% of the basic salary, tax deduction which is 16% of the basic salary. Compute and display also the total deductions by adding all deductions (SSS, PAG-IBIG, PhilHealth, and tax). Compute and display the net pay by subtracting total deductions from basic salary.

flowchart TD
    start(["Start"])
   init{{num = 0<br>rate = 0<br>hour = 0<br>basicSalary = 0<br>sss = 0<br>pagibig = 200<br>philhealth = 0<br>tax = 0<br>netPay = 0<br>deduction = 0<br>}}
    input[Input num, rate, hour]
   process["basicSalary = rate * hour<br>sss = 0.2 * basicSalary<br>philhealth = 0.05 * basicSalary<br>tax = 0.16 * basicSalary<br>deduction = sss + philhealth + pagibig + tax<br>netPay = basicSalary - deduction<br>"]
    output[Output basicSalary, sss, pagibig, philhealth, tax, deduction, netPay]
    terminus(["End"])

    start --> init
    init --> input
    input --> process
    process --> output
   output --> terminus

Solution

netpay.cpp

#include <iostream>
using namespace std;
 
int main () {
  int employeeNum = 0, ratePerHour = 0, hoursWorked = 0;
  int basicSalary = 0, sss = 0, philhealth = 0, pagibig = 200,  tax = 0, deduction = 0, netPay = 0;
  
  cout << "Please enter your employee number: ";
  cin >> employeeNum;
  cout << "Please enter the rate per hours worked: ";
  cin >> ratePerHour;
  cout << "Please enter the amount of hours in service: ";
  cin >> hoursWorked;
  
  basicSalary = ratePerHour * hoursWorked;
  sss = basicSalary * 0.2;
  philhealth = basicSalary * 0.05;
  tax = basicSalary * 0.16;
  deduction = sss + pagibig + philhealth + tax;
  netPay = basicSalary - deduction;
  
  cout << "Your base salary is " << basicSalary << endl;
  cout << "Your deductions are: \n\tSSS: " << sss << "\n\tPhilHealth: " << philhealth << "\n\tPAG-IBIG: " << pagibig << "\n\t16% tax: " << tax << endl;
  cout << "Your total deductions amount to: " << deduction << endl;
  cout << "Your net pay is: " << netPay;
  return 0;  
}