1.2. Programming Basics#

Assuming that you have some experience programming earlier, in this section we will recap on basic programming concepts using C++. Since we assume your first exposure to programming was in C, we may compare C++ to C.

1.2.1. Basic Structure of a C++ Program#

In Fig. 1.2, we show an example of a C++ program that prints Hello world!.

#include <iostream> is an include statement that includes the standard input-output stream library. iostream has implementations of streams, which are a sequence of characters transferred between the program and input-output devices. We will use cout and cin, where cout is for output and cin is for input. The equivalent of #include <iostream> is #include <stdio.h> in C.

using namespace std; is a statement that declares using a container of names named std. Here, namespace means a container and std is the container we will use. std is short for standard.

int main (){ is the main function which is the first function called when executing our program.

cout is a standard output stream that we use to write output to the screen.

<< is an operator. Just like + is an operator for addition, << is an operator to output.

"Hello world!" is a string that we want to output. Note that we have it between double quotes.

<< endl; is the output operator << again followed by endl, which is used to output a newline in C++.

return 0; exits the main function just as in C.

Recall that in C, the above program would look as follows:

Code


#include <stdio.h>
int main(void){
  printf("Hello world!\n");
  return 0;
}

1.2.1.1. A program to input a value#

If we would like to write a program that takes a number from the user, we would use cin as follows.

Code


#include <iostream>
using namespace std;


int main(void) {
  int value = 0;
  cout << "Enter a value: ";

  cin >> value; // operator to input is >> 

  cout << "The value entered is " << value << endl;
  return 0;
}

In line 5, we declare an integer variable named value as we would do in C.

In line 8, cin is standard input stream used to get user input, and >> is the operator used to get the user input and store it in the variable to the right of >>, which is value.

In line 10, we use cout to output the string "The value entered is " followed by value. To follow the string by the value stored in a variable, you have to put a << before the variable.

Equivalent in C

The above program in C looks as follows.

Code


#include <stdio.h>



int main(void) {
  int value;
  printf("Enter a value: ");
  scanf("%d", &value);
  printf("The value entered is %d\n", value);
  return 0;
}

In line 6, we used scanf function to take input from the user.

In C, we have to use format specifiers, e.g. %d, to specify the type of the variable to print it or to take it as input. Note that this is not the case in C++.

Tip

Many people are confused about when to use << and >>. Our tip is to consider the direction in which the operators point. If you are using cout, you use << which points outside the page towards cout. Otherwise, if you are using cin, then use >> which points inside the page towards the variable that we are reading into. This is illustrated in the figure below.

Direction of operator — Fig. 1.3 Direction of the operator can help you recall its use.#

1.2.2. Common Data Representations#

In C and C++, we define the data type of a variable when we declare it, e.g. in int i;, we declare a variable i of int type. The data types in C++ are similar to C. In the following subsections, we recap on common data types in C++.

1.2.2.1. Integers#

Integers are whole numbers, for example, \(0\), \(-23\) and \(789\). We have different data types to store an integer.

int stores an integer typically in 32 bits, i.e. 4 bytes. Recall that 8 bits make a byte. If one bit stores the sign, we have 31 bits to store the number. Hence, int can store \(-2^{31}\) to \(0\) to \(2^{31} - 1\).
short stores an integer typically in 16 bits. If one bit stores the sign, we have 15 bits to store the number. Hence, short can store \(-2^{15}\) to \(0\) to \(2^{15} - 1\).
long stores an integer typically in more than 32 bits with obviously a wider range of numbers.

For the purpose of this course, we recommend using int to store integers. For example, int participants = 60;

1.2.2.2. Floating-point numbers#

Floating-point/fractional/real numbers are numbers that have numbers after the decimal point, for example, \(2.9\), \(-118.763\). The floating-point representation in computer memory resemble scientific notation., e.g. \(2.89 \times 10^{14}\) is represented as \(2.89e14\) or \(2.89E14\). Different data types in C/C++ can store floating-point numbers.

float stores a number using 32 bits, with 7 decimal digits of precision — the total number of significant digits both before and after the decimal point.
double stores a number using 64 bits, with 15 decimal digits of precision.
long double typically stores a number using more than 64 bits, with greater precision than double.

For the purpose of this course, we recommend using double to store floating-point numbers. For example, double inchesInCm = 2.54;

1.2.2.3. Boolean#

Similar to C, in C++, we have the bool data type to represent a logical value, i.e. true or false in 8 bits. Different from C, in C++, we don’t need to include a library to use this data type. For example, bool isRaining = false;

1.2.2.4. Characters#

We can store a single character in char data type using 8 bits. For example, char letter = 'a', char sign = '-' where the character is enclosed between a single quote.

1.2.2.5. Arrays#

An array stores multiple data elements of the same data type using a single identifier. Data can be of any type. For example, in

int arr[7] = {1, 2, 3, 4, 5, 6, 7};

arr is an array identifier that represents 7 different elements of the data type int. arr[0] would access the first element storing 1. The last element can be accessed using arr[6].

1.2.2.6. Strings#

An array can be used to store more than a single character. This can be a string in C if it was a null-terminated array of characters. For example, in

char h[6] = "Hello";

we declare a string named h that stores the string "Hello", where h[5] stores a null character '\0'.

In C, including the string library using #include <string.h> can give access to string functions like strcmp, strlen and strcpy.

However, in C++, we have a data type named string to store a sequence of characters. To use this data type, you need to include the string library using #include <string>. You can perform some operations on strings such as concatenating them using + or comparing them using ==. For example, in the following code, we take from the user the course department and code and check if it is "ECE244".

Code


#include <iostream>
#include <string>


using namespace std;


int main(void) {
  string prePhrase = "This course is ",
         postPhrase = " Programming Fundamentals!", blank = "________";
  cout << "Fill in the blank of the following sentence" << endl;
  cout << prePhrase << blank << postPhrase << endl;
  cin >> blank;
  if (blank == "ECE244") {
    cout << "Correct!" << endl;
    string sentence = prePhrase + blank + postPhrase;
    cout << sentence << endl;
  } else {
    cout << "Incorrect!" << endl;
  }
  return 0;
}

1.2.3. Operators#

Like most programming languages, in C++, we have:

Arithmetic operators such as +, -, *, / and % with brackets () to help us define the precedence of operations. For example, 5 % 3 is the remainder of 5 divided 3 is 2.
Assignment operators which assigns an evaluation/value to a variable. For example, in int x = 7 + 3; the = assigns the value of 7 + 3 to x. In addition to =, we have +=, -=, *=, /= and %=. These assign to the variable on the left the variable itself plus/minus/multiplied/divided/modulo the value on the right. For example, x += 3 is equivalent to x = x + 3.
Increment and decrement operators such as ++ and --. For example, i++; would increment i by 1.
Relational operators such as == (equal), != (not equal), < (less than), > (greater than), <=(less than or equal), >= (greater than or equal) that compare two values and get evaluated to true or false. For example, 7 < 5 would be evaluated as false.
Logical operators such as && (and), || (or) and ! (not). For example, if we want to evaluate a number is between 5 and 15 (inclusive), then the number has to be greater than or equal 5 and less than or equal 15. This would translate to this expression number >= 5 && number <= 15.
sizeof() operator would find the number of bytes it takes to store a data type. For example, sizeof(int) would evaluate to 4, as it takes 4 bytes to store an int.

1.2.4. Control Structures#

Control structures are used to control the flow of execution of a program, e.g., if-statements and while, for and do-while loops.

1.2.4.1. If-statements#

In C and C++, if-statements allow you to take a decision in a program to do something if a condition is true. If we want to take another decision if the condition is false, an else to the if would do it. For example, in the following code, we try finding out if the shape is a rectangle or square based on the height and width entered by the user.

Code


#include <iostream>


using namespace std;


int main(void) {
  int height = 0, width = 0;
  cout << "Please enter the height and width of your shape: ";
  cin >> height >> width;

  if (height == width) {
    cout << "The shape is a square." << endl;
  } else {
    cout << "The shape is a rectangle." << endl;
  }
  return 0;
}

1.2.4.2. Loops#

On the other hand, loops help you execute a block of code repeatedly as long as a condition is true. There are three main loop structures:

In a while loop, if the condition is true, the body of the loop will be executed. Otherwise, statements after the loop are executed. The body of the loop will be executed repeatedly until the condition returns false. For example, the following code prints numbers from 1 to 10.

Code
```
 
 #include <iostream>
 

 using namespace std;
 

 int main(void) {
   int i = 1;
   while (i <= 10) {
     cout << i << " ";
     i++;
   }
   cout << endl;
   return 0;
 }
 
 
```
A do-while loop executes the body of the loop first then checks the condition. If the condition is true, the body of the loop would be executed again. Otherwise, the statements after the loop will be executed. For example, the following code would ask the user to enter a number between 1 and 10, and if the entered number is within the range in line 10, it would exit the loop. Otherwise, it will continue to prompt the user in lines 8 – 9. The body of the loop will be executed at least once.

Code
```
 
 #include <iostream>
 

 using namespace std;
 

 int main(void) {
   int num;
   do {
     cout << "Please enter a number between 1 and 10 (inclusive): ";
     cin >> num;
   } while (num < 1 || num > 10);
   cout << "The number entered is " << num <<  endl;
   return 0;
 }
 
 
```
A for loop also does repeat a block of code depending on a condition, but it has a different structure with three expressions: initialization, where you initialize a state of a variable for example, condition, which determines if the program will execute the body of the loop, and increment, where you change the state of the variable to get closer to change the condition. For example, in line 6 in the code below, int i = 1 initializes i to 1, i <= 10 checks if i is less than or equal to 10, and in i++ we increment i by 1. The body of the for loop is executed as long as i is less than or equal to 10.

Code
```
 
 #include <iostream>
 

 using namespace std;
 

 int main(void) {
   for (int i = 1; i <= 10; i++) {
     cout << i << " ";
   }
   cout << endl;
   return 0;
 }
 
 
```

Khufu: Object-Oriented Programming using C++

Programming Basics

Contents

1.2. Programming Basics#

1.2.1. Basic Structure of a C++ Program#

1.2.1.1. A program to input a value#

1.2.2. Common Data Representations#

1.2.2.1. Integers#

1.2.2.2. Floating-point numbers#

1.2.2.3. Boolean#

1.2.2.4. Characters#

1.2.2.5. Arrays#

1.2.2.6. Strings#

1.2.3. Operators#

1.2.4. Control Structures#

1.2.4.1. If-statements#

1.2.4.2. Loops#