Polyalphabetic Encryption C / C++

This program is for implementing Poly-Alphabetic Encryption. This is a part of Mumbai University MCA Colleges Data Communication and Networking MCA Sem 4

#include<stdio.h>

#include<conio.h>

#include<string.h>

void main()

{

            int i,j=0;

            int tmp1,tmp2;

            int dtln,kln,sum;

            char data[100],key[100],cipher[100];

            clrscr();

            printf("Enter String : ");

            gets(data);

            printf("Enter Key : ");

            gets(key);

            dtln=strlen(data);

            kln=strlen(key);

// Sender Side

            for(i=kln;i<dtln;i++)

            {

                        if(data[i]==32)

                        {

                                    i++;

                        }

                        key[i]=key[j];

                        j++;

            }

            for(i=0;i<dtln;i++)

            {

                   if(data[i]==32)

                   {

                        cipher[i]=' ';

                        i++;

                   }

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

                   {

                                    tmp1=data[i]-65;

                   }

                   else if(data[i]<=123 && data[i]>=97)

                   {

                                    tmp1=data[i]-97;

                   }

                   tmp2=key[i]-64;

                   sum=tmp1+tmp2;

                   if(sum>26)

                   {

                                    sum=sum-26;

                                    cipher[i]=sum+64;

                   }

                   else

                   {

                                    cipher[i]=sum+64;

                   }

            }

            cipher[i++]='\0';

            puts(cipher);

//RECEIVER SIDE

            printf("Receiver Side\n");

            for(i=0;cipher[i]!='\0';i++)

            {

                   tmp1=cipher[i]-64;

                   tmp2=key[i]-65;

                   sum=tmp1-tmp2;

                   if(sum<0)

                   {

                                    sum=sum+26;

                                    cipher[i]=sum+64;

                   }

                   else

                   {

                                    cipher[i]=sum+64;

                   }

            }

            cipher[i++]='\0';

            printf(“\n\nCipher Text :”);

            puts(cipher);

            getch();

}

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