cryptography in c on linux

This program takes a text file from guest file and encrypts it.to retain the original text redo the same code.you can make the algorithm more abstruse.try it.for example as key ,which here is taken as i=i+2.you can take a song(dat file) converted to text file.or you can first invert the source text then encrypt.
Code;-

#include<stdio.h>
int main()
{unsigned long int i=0;
 char ch;
 char name1[20],name2[20];
 FILE *fp,*ft;
 printf("ENTER THE SOURCE FILE:");
 gets(name1);
 printf("ENTER THE DESTINATION FILE:");
 gets(name2);
 fp=fopen(name1,"r");
 ft=fopen(name2,"w");
 if(fp==NULL)
 {printf("CAN,T OPEN THE FILE");
  }
 while(!feof(fp))
 {ch=getc(fp);
  ch=~((ch^i));
  i+=2;
  if(i==100000)
  {i=0;
   }
  putc(ch,ft);
  }
  fclose(fp);
  fclose(ft);
  return 0;
}