The Complete Codes

Mono Alphabetic Cipher Encryption-Decryption Introduction It is Better than Caesar Cipher. If, instead the “cipher” line can be any permutation of the key 26 alphabetic characters, then there are 26! Or greater than 4 * 10 26  possible keys. This is 10 orders of magnitude greater than the key space for DES and would seem to as a Mono-alphabetic substitution cipher, because a single cipher alphabet is used per message. There is however, another line of attack. If one analytically knows the nature of the plain text, then the analyst can exploit the regularities of the language. Limitations Monoalphabetic ciphers are easy to break because they reflect the frequency data of the original alphabet. A countermeasure is to provide multiple substitutes, known as homophones, for a single letter C Progrm to Encryp the imputed text using Mono Alphabetic Cipher. #include <stdio.h> #include <string.h> int main () {     char pt [ 52 ] = { 'A' , 'B' , 'C' ,

Recurrences And Their Solution Methods Recursion Tree Just Simplification of Iteration method: Consider The Recurrences Second Example Example Three Master Method Cookbook solution for some recurrences of the form T(n) = a . T(n/b) + f(n) where a>=1, b>1, f(n) asymptotically positive Describe its cases 

Recurrences Recursive algorithms are described by using recurrence relations. A recurrence is an inequality that describes a problem in terms of itself. For Example: Recursive algorithm for finding factorial   T(n)=1     when n =1 T(n)=T(n-1) + O(1)    when  n>1 Recursive algorithm for finding Nth Fibonacci number T(1)=1     when n=1 T(2)=1     when n=2 T(n)=T(n-1) + T(n-2) +O(1)     when n>2 Recursive algorithm for binary search T(1)=1     when n=1 T(n)=T(n/2) + O(1)    when n>1 Techniques for Solving Recurrences We’ll use four techniques: Iteration method Recursion Tree Substitution Master Method   – for divide & conquer Characteristic Equation   – for linear Iteration method Expand the relation so that summation independent on n is obtained. Bound the summation e.g.    T(n)= 2T(n/2) +1  when n>1 T(n)= 1    when n=1 T(n) = 2T(n/2) +1           = 2 { 2T(n/4) + 1} +1           = 4T(n/4) + 2 + 1           =

C Program To Check The String Is Valid Identifier Or Not #include <stdio.h> #include <conio.h> #include <string.h> int main () { char string [ 25 ]; int count= 0 ,flag; printf ( "Enter any string: " ); gets (string); if ( ( string [ 0 ]>= 'a' && string [ 0 ]<= 'z' )||( string [ 0 ]>= 'A' && string [ 0 ]<= 'Z' )||( string [ 0 ]== '_' )) {     for ( int i= 1 ;i<= strlen (string);i++)     {         if (( string [i]>= 'a' && string [i]<= 'z' )||( string [i]>= 'A' && string [i]<= 'Z' )||( string [i]>= '0' && string [i]<= '9' )||( string [i]== '-' ))     {     count++;     }        }     if (count== strlen (string))     {       flag= 0 ;     } } else {     flag= 1 ; } if (flag== 1 )     printf ( " %s is not valid identifier" ,string); else     printf ( " %s is valid ident