Char Data Type, Character Arrays & C++ Strings

Agenda

Char data type
Functions on Char

Char Array / C-Style Strings
String Literals
Functions on Char Array

C++ Strings
Functions on Strings

Character Datatype

The char data type is used to store a single character.

The character must be surrounded by single quotes, like 'A' or 'c':

LIVE DEMO

ASCII was the first character set (encoding standard) used between computers on the Internet.

ASCII is a 7-bit character set containing 128 characters.
It contains the numbers from 0-9, the upper and lower case English letters from A to Z, and some special characters.

🚀 ASCII Character Set

LIVE DEMO

Character Functions - <cctype> library

isaplha(c)

isdigit(c)

islower(c)

isupper(c)

isspace(c)

. . .

https://www.cplusplus.com/reference/cctype/

Testing Functions

Character Functions - <cctype> library

toupper(c)

tolower(c)

Conversion Functions

LIVE DEMO

Reading a Char using cin.get() vs cin

cin.get() reads all possible type of characters including whitespaces.

Generally, cin with an extraction operator (>>) terminates when whitespace is found. However, cin.get() reads a string with the whitespace.

Shortest Path

Suppose you want to go to a location, located at (X,Y) starting from origin (0,0). Your friend tells you a long way by telling the steps you should walk in each direction (N,W,E or S). Find the shortest path. Input & Output is a string. Refer Example:

Input: NNNEEWS

Output: NNE

ABCD Pattern

Print a pattern of the following form.

ABBA

ABCCBA

ABCDDCDA

Arrays of Characters /

C-Style Strings

Sequence of characters stored in continguous memory (character array)
Need to explicitly terminate by a null character.
Character Arrays support read, write & update.

🚀 C-Style Strings / Char Array

Sequence of characters written in double quotes.
Stored in read only memory
Terminated by a Null Character

String Literals

Understanding the term "null-terminated"

char name[ ] {"Prateek"}

Problems
- Can't add more letters to an array

🚀 Creating String Variables (Char Array)

char name[10] {"Hello World"}

🚀 Creating String Variables (Char Array)

char name[10];

🚀 Creating C-style String Variables (Char Array)

name = "Prateek"; //Error array name and string literal are location in memory

strcpy(name, "Prateek") // Allowed

char name[10];  //no null initialisation by default

🚀 Functions for C-style String Variables

Length
Copy
Concatenation
Searching
and more

char name[10];

Input using "cin"
Input using "cin.get()"
Input using "getline()"

🚀 Input/Output

char name[10];  //no null initialisation by default

Printing name can possibly print garbage letters until a null is found in the memory.

So either initialise the array, using a string literal or take input from the user.

🚀 Input/Output

🚀 Live Demo

//Include the Header file
#include<cstring>

char str[100];

strcpy(str, "Hello"); //Copy
strcat(str," world"); // Concatenatio
cout << strlen(str) <<endl; // length
strcmp(str, "anothe string"); //comparison

cstdlib

#include<iostream>
using namespace std;


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

Recap

cstring proivides functions to operate on character arrays.

cctype provides us functions to operate on characters.

LIVE DEMO

C++ Strings

string class available in C++ Standard Template Library.

contiguous in memory
dynamic size can grow & shrink during run time ⭐️
better than character arrays, due to fixed size of char arrays
support lot of useful member functions, no need to write functions from scratch
support operators like (+, =, <, <=, ==, != , [] ...)
safer, provide methods for bound checking

#include<string>
using namespace std;


string s1;
string s2{"Hello"};
string s3{s2};
string s4{"Hello",3}; //Hel
string s6{s2, 0,2} // He

string s5(3,'X'); //XXX

String Initialisation

#include<string>
using namespace std;


string s1;

cin>>s1;

getline(cin,s1); //Reads and stores in s1

getline(cin,s1,'$'); //Reads and stores in s1

String Input cin vs getline()

#include<string>
using namespace std;


string s1;
s1 = "Hello World";

string s2 = "Hi";
s2 = s1;  //Overwrite

String Assignment = Operator

#include<string>
using namespace std;


string firstname = "Prateek"
string lastname = "Narang"

string fullname = firstname + " " + lastname;

String Concatenation + Operator

#include<string>
using namespace std;


string firstname = "Prateek"
string lastname = "Narang"

firstname.at(0)
firstname[0]

String Accessing Characters

#include<string>
using namespace std;


string firstname = "Prateek"
string lastname = "Narang"


for(char c:firstname){
	cout << c <<endl;
}

for(int c:firstname){
	cout << c <<endl;
}

Range Based Loops

Comparison, Concatenation Operators

Substrings

string_object.substr( index, length);

Find

string_object.find(other_string);

Concatentation

+=

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

// 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

//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

🚀 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

//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

232

34543

4567654

567898765