Playfair Cipher in C

Hello friends, I am very happy to write my first post about implementation of Playfair cipher algorithm in c. 

For any query regarding c/c++ feel free to contact me on khimanichirag@gmail.com. I try my best to solve it.

     #include<stdio.h>   
     #include<conio.h>  
     #include<string.h>  
     #include<graphics.h>  
     void line(int a)  
     {  
          int i;  
           printf("\n");  
           for(i=0;i<a;i++)  
           {  
                printf("*");  
           }  
           printf("\n");  
     }  
     char s[30];  
     void main()  
     {  
         char c[27],k[30],temp[40],matrix[5][5],first,second;  
         int i,index,j,t,t1,p,p1,gd,gm;  
         initgraph(&gm,&gd, "c:\\tc\\bgi");  
         clrscr();  
         cleardevice();  
 //-------------------------ABCD in c[]---------------------------------  
         setcolor(2);  
         outtextxy(400,460,"Prepared By:Khimani Chirag");  
         setcolor(2);  
         outtextxy(150,10,"Welcome To Playfair Cipher Encryption");  
         for(i=97;i<=122;i++)  
         {  
               c[i-97]=i;  
         }  
 //---------------------------------------------------------------------  
           printf("\n\n");  
           line(50);  
           printf("enter the plain text: ");  
           gets(s);  
           printf("\nenter key for playfair cipher: ");  
           gets(k);  
           line(50);  
 //---------------------------put c[]<--* when key-----------------------  
           for(i=0;k[i]!='\0';i++)  
           {  
              index=k[i]-97;  
                if(c[index]=='*')  
                {  
                   k[i]='*';  
                }  
                else  
                {  
                   c[index]='*';  
                }  
           }  
 //------------------------------put key[] in variable-------------------  
         i=0;  
         j=0;  
           while(k[i] !='\0')  
           {  
             if(k[i]!='*' )  
             {  
                   temp[j]=k[i];  
                   j++;  
             }  
               i++;  
           }  
 //-----------------------------put c[] in temp variable------------------            
         i=0;  
         while(c[i] !='\0')  
           {  
                 if(c[i]!='*' && c[i]!='j' )  
                 {  
                 temp[j]=c[i];  
                 j++;  
                 }  
                 i++;  
           }  
          printf("\nyour matrix is:\n");  
          line(20);  
 //-----------------------------matrix printing---------------------------  
         t=0;  
         for(i=0;i<5;i++)  
         {  
                printf("*  ");  
               for(j=0;j<5;j++)  
               {  
                 printf("%c ",temp[t]);  
                 matrix[i][j]=temp[t];  
                 t++;  
               }  
                   printf("  *");  
                   if(i!=4)  
                        printf("\n");  
          }  
          line(20);  
          printf("\nyour cipher text is: ");  
 //------------------------------------------------------------------------  
         i=0;  
            if(strlen(s)%2!=0)  
            {  
               while(s[i]!='\0')  
               {  
                    i++;  
               }  
               s[i]='x';  
               s[i+1]='\0';  
            }  
           for(index=0;index<strlen(s);index+=2)  
           {  
                 first=s[index];  
                 second=s[index+1];  
              for(i=0;i<5;i++)  
              {  
                   for(j=0;j<5;j++)  
                   {  
                        if(matrix[i][j]==first)  
                       {  
                             t=i;  
                             t1=j;  
                       }  
                       if(matrix[i][j]==second)  
                       {  
                            p=i;  
                            p1=j;  
                       }  
                   }  
              }  
               if(p==t)  
               {  
                    if(p1==4)  
                    {  
                     p1=-1;  
                    }  
                    if(t1==4)  
                    {  
                      t1=-1;  
                    }  
                   printf("%c%c",matrix[t][t1+1],matrix[p][p1+1]);  
               }  
               else if(p1==t1)  
               {  
                    if(p==4)  
                    {  
                          p=-1;  
                    }  
                    if(t==4)  
                    {  
                      t=-1;  
                    }  
                    printf("%c%c",matrix[t+1][t1],matrix[p+1][p1]);  
               }  
               else  
               {  
                   printf("%c%c",matrix[t][p1],matrix[p][t1 ]);  
               }  
         }  
         getch();  
     }