C Code 35 _ To Perform Encryption and Decryption using Caesar Cipher

C Code 35 _ To Perform Encryption and Decryption using Caesar Cipher 

Sample Input:

Message to Encrypt  :  abcd

Shifting value : 2

Sample Output:

Encrypted Message  :  cdef

Explanation:

According to the shift value right we need to shift each character.

if we shift ' a ' two times right we get ' c ' , simillarly if we shift ' y ' two times right we get ' a ' and so on.

Simillarly for decryption we need to shift  value left .

if we shift ' d ' one time left we get ' c ' and if we shift ' a ' one time left we get ' z ' and so on.

Program:

#include<stdio.h>

int main()

{

                char str[200],stre[200];

                int n,i=0,m,ch;

                printf("* * * Encryption and Decryption of a Message using Caesar Cipher * * *");

                printf("\n\n1 - Encryption\n2 - Decryption\n\nEnter Your Choice : ");

                scanf("%d",&ch);

                switch(ch)

                {

                                case 1:

                                                printf("\n\nEnter a String to encrypt : ");

                                                fflush(stdin);

                                                gets(str);

                                                printf("\n\nEnter a shift value(number) : ");

                                                scanf("%d",&n);

                                                while(str[i]!='\0')

                                                {

                                                                if(str[i]==32)

                                                                {

                                                                                stre[i]=str[i];

                                                                                i=i+1;

                                                                }

                                                                else

                                                                {

                                                                                if(str[i]>=65&&str[i]<=90)

                                                                                {

                                                                                                m=(int)str[i]-65;

                                                                                                m=(m+n)%26;

                                                                                                stre[i]=m+65;

                                                                                }

                                                                                else if(str[i]>=97&&str[i]<=122)

                                                                                {

                                                                                                m=(int)str[i]-97;

                                                                                                m=(m+n)%26;

                                                                                                stre[i]=m+97;

                                                                                }

                                                                                else

                                                                                {

                                                                                                stre[i]=str[i];

                                                                                }

                                                                                i=i+1;

                                                                }

                                                }

                                                stre[i]='\0';

                                                printf("\n\nEncrypted string : %s",stre);

                                                break;

                               

                                case 2:

                                                printf("\n\nEnter a String to decrypt : ");

                                                fflush(stdin);

                                                gets(stre);

                                                printf("\n\nEnter a shift value(number) : ");

                                                scanf("%d",&n);

                                                while(stre[i]!='\0')

                                                {

                                                                if(stre[i]==32)

                                                                {

                                                                                str[i]=stre[i];

                                                                                i=i+1;

                                                                }

                                                                else

                                                                {

                                                                                if(stre[i]>=65&&stre[i]<=90)

                                                                                {

                                                                                                m=(int)stre[i]-65;

                                                                                                m=(m-n)%26;

                                                                                                if(m<0)

                                                                                                {

                                                                                                                m=m+26;

                                                                                                }

                                                                                                str[i]=m+65;

                                                                                }

                                                                                else if(stre[i]>=97&&stre[i]<=122)

                                                                                {

                                                                                                m=(int)stre[i]-97;

                                                                                                m=(m-n)%26;

                                                                                                if(m<0)

                                                                                                {

                                                                                                                m=m+26;

                                                                                                }

                                                                                                str[i]=m+97;

                                                                                }

                                                                                else

                                                                                {

                                                                                                str[i]=stre[i];

                                                                                }

                                                                                i=i+1;

                                                                }

                                                }

                                                str[i]='\0';

                                                printf("\n\nDecrypted string : %s",str);

                                                break;

                                               

                                default:

                                                printf("\n\nEnter a valid choice 1 or 2 only");

                }

                return 0;

}

Output:

Thank You ...

To learn c : https://iamafutureprogrammer.blogspot.com/p/blog-page_23.html  

How Internet Works :  https://iamafutureprogrammer.blogspot.com/p/how-internet-works.html