C++ Getting Started

Hello World!

  • Boilerplate
  • Building and running a C++ Code

C++ Boilerplate

#include<iostream>
using namespace std;


int main(){
	// Your code logic goes here
	return 0;
}

C++ Hello World

#include<iostream>
using namespace std;


int main(){
	cout<<"Hello World!";
	return 0;
}

LIVE DEMO

Next Step - Solve a Problem !

🚀 Average the Marks

Given marks of a student in 3 subjects - Physics, Chemistry and Maths - print their average.

 

Sample Input

Physics = 90

Maths = 75

Chemistry = 68

 

Sample Output

77.66

C++ Digger Deeper

Digging Deeper ...

  • Preprocessor Directive
  • Keywords
  • Identifiers
  • main()
  • Namespaces
  • The preprocessors are the directives, which give instructions to the compiler to preprocess some code before actual compilation starts.
  • The directive begins with '#'
  • The actual code is compiled by compiler only.

🚀 Preprocessor Directive

#include

directive tells the compiler to include the header file in the source code.

 

 
#include<iostream>
#incldue<algorithm>
#include<stack>


int main(){
	
    ....

}
#define

directive tells the compiler to create symbolic constants. The symbolic constant is called a macro.

 

All subsequent occurrences of macro in that source code will be replaced by its replacement text before the program is compiled.

#define PI 3.14

int main(){
	//Area of Circle
 	int r = 5;
 	float area = PI*r*r;

	return 0;
}
#define

directive tells the compiler to create symbolic constants. The symbolic constant is called a macro.

 

All subsequent occurrences of macro in that source code will be replaced by its replacement text before the program is compiled.

#define PI 3.14
#define AREA(l,b)  (l*b)

int main(){
	//Area of Rectangle
	int area = AREA(10,5);

	return 0;
}
  •  Both an identifier and a variable are the names allotted by users to a particular entity in a program.

 

  • The identifier is only used to identify an entity uniquely in a program at the time of execution whereas, a variable is a name given to a memory location, that is used to hold a value.​

🚀 Identifiers


float calculateMarks(int p,int c, int m){
  	float average = (p+c+m)/3;
  	return average;
}

Identify the Identifiers

  • Keywords are the word that have a special meaning for the compiler.
  • These keywords can't be used as an identifier.
  • C++ has about 95 reserved words.

🚀 Keywords

auto    double  int struct
break   else    long    switch
case    enum    register    typedef
char    extern  return  union
const   float   short   unsigned
continue for    signed  void
default goto    sizeof  volatile
do  if  static  while
32 Keywords common in C++ and C

 

asm dynamic_cast    namespace   reinterpret_cast
bool    explicit    new static_cast
catch   false   operator    template
class   friend  private this
const_cast  inline  public  throw
delete  mutable protected   true
try typeid  typename    using
using   virtual wchar_t
Some new Keywords in C++
int factorial(int n){
	
    if(n<0){
    	cout << "Invalid Input";
        return -1;
    }
    
    int ans = 1;
    for(int i=1;i<=n;i++){
    	ans = ans*i;
    }
	
    return ans;
}

Identify the Keywords

Main Function

  • Every C/C++ Program stars executing with main.
  • There is exactly 1 main function.
  • return 0, indicates successful execution of main.

🚀 main() function


int main(){
	//Execution stars from here
	// Your Work

	return 0;
}
int main(){
    //logic


    return 0;
}

Most common way

int main(int argc,char *argv[]){
    //logic

    return 0;
}

Command Line Apps

  • main is not a keyword in C/C++.
  • main is not predefined, but it is predeclared.
  • In C++, your code is linked against a small runtime library that constitutes the true starting point of your program.
  • It is this small library calls a function called main--it's hardcoded to do so.
  • Your code runs because you supply the code inside main, also called function definition.

Main Recap

  • Naming conflicts can arise if you use multiple 3rd party libraries in same program.​
  • Namespaces are used to resolve naming conflicts.
  • std is the name for the standard C++ Namespace.
  • Writing std::cout will tell the compiler to use "cout" from standard namespace.

 

🚀 Namespaces

Third party Namespace

using namespace cv;

 

 To avoid data structure and function name conflicts with other libraries, OpenCV has its own namespace: cv.

#include <opencv2/opencv.hpp> 
#include <iostream>
using namespace cv;
using namespace std;

int main(int argc, char** argv) 
{ 

 cout<<"Welcome to Image Editing App";

 Mat image = imread("Bob.jpg"); 
 
 
 return 0; 
}

Example of Third Party Namespace

  •  Comment is text that  is normally used to annotate code for future reference.
  •  Comment is ignored by compiler but that is useful for programmers.
  •  You can use comments in testing to make certain lines of code inactive.
  • We can write single line or multi-line comments in a C++ Program.

🚀 Comments

🚀 Summary

 

  • Keywords have special meaning for the compiler.
  • Identifiers are used to name an entity, variable name is also a type of identifier.
  • Header files include some pre-written code required to execute our program.
  • Program execution always starts with main()
  • { } are used to enclose a block (function, if, while etc.}.
  • C++ Compiler Ignores whitespace (space, carriage returns, linefeeds, tabs, vertical tabs, etc.)
  • Output using cout
  • Input using cin
  • Comments (// & /*… */)
  • Every statement must end with a semicolon ;

 

 

Variables & Constants

Variables

Variable name: A label for a memory location

Value: The something that would be

stored in a variable

Storage: A place where data can be stored

Declaration: Announcing a variable (usually) at the beginning of a program

Naming convention: A set of rules about the names of variables

Assignment: Giving (setting) a variable a value

🚀 Variables

🚀 Naming Variables

  • For variable name we can use uppercase and lowercase letters, digits from 1 to 9 and underscore(_).

 

  • First character must be underscore or letter.

 

  • C++ is strongly typed language. So every variable needs to be declare before using it.

 

//Valid Names
double simple_interest;

int student_age;
float Student_percentile;
int prateek123;


//Invalid Names
int 123_age;
  • Variables when just declared have garbage value until they are assigned a value for the first time.

 

  • We can assign a specific value from the moment variable is declared, called as initialization of variable.
//Initialisation of Variable
float a = 10;

//Declaration
int b;
//Assignment
b = 20;

Initialisation

🚀 Data-types

Boolean - boolean
Character - char
Integer – int
Floating Point – float 
Double Floating Point – double

🚀 Binary Number System

🚀 Data-type Modifiers

Several of the basic types can be modified using one or more of these type modifiers

 

signed
unsigned
short
long


int marks;
unsigned int roll_number;
unsigned long long int large_factorial;


short int age;

How storage works?

Constants

Constants are variables or values in programming language which cannot be modified once they are defined.

const float pi = 3.14

const int loan_period = 10

//Don't do this, Initialisation is Must for constants
const int x;
x = 5;
// Assignment is not allowed here

 

Using a const keyword

Using preprocessor directive

#define PI 3.14
#define LOAN_PERIOD 10

Operators, Statements & Expressions

Conditional Statements

Conditional Statements

// Single If

int marks = 90;

if (marks > 80) {
	cout << “Let's Party!”;
}

Conditional Statements

If-else block

// If-Else Block

int marks = 70;

if (marks > 80) {
	cout << “Let's Party”;
}
else{
	cout<< “Work hard next time“;
}

Conditional Statements

If-else-if-else block

// If-Else Block

int marks = 70;

if (marks > 80) {
	cout << “Let's Party”;
}
else if(marks>60){
	cout<<"Good Job";
}
else{
	cout<<"Work hard next time";
}

Challenge 🔥 

Electricity Bill Calculator : Given total consumption of a 

household in units, write a program to estimate the total bill amount as per the table.

Units Charges
1 to 100 units  Free
100 to 200 units Rs. 5/unit
200 to 300 units Rs.10/unit
300+ units Rs.12/unit

Ternary Operator

Switch Case

switch(expression) {
  case x:
    // code block
    break;
  case y:
    // code block
    break;
  default:
    // code block
}

Loops

While Loop

While Loop

//Init 

while(..condition is true ..){
	
    //execute some stuff
    
    //update 
}

Examples! 👨‍💻

For Loop


for(init;stopping_condition;update_statement){
    //execute some stuff
}

For Loop


for(int calories=0;calories<100;calories = calories+1){
	
    //execute some stuff
    cout<<"Run 1 step";
    
}

Examples! 👨‍💻

 

Given N, Print following pattern (For Example N = 5)

 

    *

   ***

  *****

 *******

🚀  Challenge - Star Pyramid

🚀  Challenge - ABCD Pattern

 

Given N, Print following pattern (For Example N = 5)

 

ABCDEEDCBA
ABCDDCBA
ABCCBA

ABBA

AA

 

 

 

🚀  Print All Prime

 

Given N, Print all Prime Numbers upto N.

 

For Example - N = 10

 

Output - [2,3,5,7]

Do While Loop


//init 

do(){
    //execute some stuff
    
   
}
while(condition);

Do While Loop  vs While

Do While Loop  vs While

//init 
do(){
    //execute some stuff
    
   
}
while(condition);
//Exit Controlled Loop
//init 
//Entry Controlled Loop
while(condition){
    //execute some stuff
    
   
}

Break and Continue

int calories = 0;
while(calories<20){

	if(calories==15){
    		cout<<"Stop the Workout";
    		break;
	}
    
	cout<<calories<<" ";
	calories = calories + 1;
}	

cout<<"Complete";

int calories = 0;
while(calories<20){

	if(calories==15){
    		cout<<"Stop the Workout";
    		calories = calories + 1;
    		continue;
	}
	cout<<calories<<" ";
	calories = calories + 1;
}	

cout<<"Complete";

Break Statement

int calories = 0;
while(calories<20){

	if(calories==15){
    		cout<<"Stop the Workout";
    		break;
	}
    
	cout<<calories<<" ";
	calories = calories + 1;
}	

cout<<"Complete";

Stop the loop when executed.

 Continue Statement

int calories = 0;
while(calories<20){

	if(calories==15){
    		cout<<"Go to the next Step";
    		calories = calories + 1;
    		continue;
	}
	cout<<calories<<" ";
	calories = calories + 1;
}	

cout<<"Complete";

Control jumps to the beginning of the loop for next iteration

Practice Problems

  • Print all Fibonacci number less than N

 

 

  • Write code to print the following pattern

       1

     232

   34543

 4567654

567898765

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