Copyright © 2022, Umar Habib, All rights reserved.

Regular-Expression-Cpp

Regular Expression in C++. You will Never have been seen Regex in C++ without using libraries. I have made Regex in C++ only | if | else | loop | with ASCII code. This program will work like key Events.

First

Declared variable

'n' variable is used to take input. 'i' variable is used to control backspace key and 'j' controls first 'if' block control. Declare empty array of type char.

    int n,i=0,j=0;		
	 char name[20]="";

Labels

These labels are used with goto statements

   b_name:
   b_Wrong_put:

While loop

Range of name is 20 character So, loop will be executed 20 times.

If Outer block

If inner

This block will be executed when we use integer as first character.

if(n>=33 && n<=64)
			{
				system("cls");
				cout<<" \t\t  Use integer value After One Character ";				
				goto b_Wrong_put;	
			}

Else If

This block will be executed when backspace key is pressed and one index is subtracted from array.

else if(n==8)
			{	
				i--;	
				name[i]='\0';           /*    '\0' is use for null value assign to any variable    */															
				system("cls");
				goto b_Wrong_put;
			}

Else If

This block will be executed when we press enter without writing anything.

else if(n==13)
			{				
					for(char a='a'; a<='z'; a++)
					{
						if(name[i]==a)
						{
							system("cls");
							break;
						}
					}									
					for(char b='A'; b<='Z'; b++)
					{
						if(name[i]==b)
						{
							system("cls");
							break;
						}							
					}
				system("cls");
				cout<<" \t\t  Don't Empty...! ";				
				goto b_Wrong_put;																											
			}

Else If

This will be executed when we use Space in the name.

else if(n==32)
			{
				system("cls");
				cout<<" \t\t    Space Not Use In Name ";
				goto b_name;
			}

Else

This will be executed when we pass value to array.

else						
			{				
				name[i]=n;
				j++;
				i++;
				system("cls");
				goto b_name;	
			}

Else Outer

If

This will be executed when pass value to array.

if(n>=48 && n<=57 || n>=65 && n<=90 || n>=97 && n<=122 )
	{
		name[i]=n;
		i++;
	}

Else If

This block will be executed when backspace key is pressed and one index is subtracted from array.

else if(n==8)
			{	
				i--;
				if(i==0)
				{
					j=0;	
				}					
				name[i]='\0';           /*    '\0' is use for null value assign to any variable    */															
				system("cls");
				goto b_Wrong_put;
			}

Else If

This will be executed when press enter key.

else if(n==13)
			{	
				system("cls");					
				break;
			}

Else If

This will be executed when we use Space in the name.

else if(n==32)
			{
				system("cls");
				cout<<" \t\t    Space Not Use In Name ";
				goto b_name;
			}

Else

This block will be executed when we use integer as first character.

else
			{
				system("cls");
				cout<<" \t\t  Only Use Character and integer value After One Character ";
				goto b_Wrong_put;
			}

Output

Name will be shown:

cout<<"\n\n\n\n\n\t\t\t\t"<<name;