Program for Encoding & Decoding a Line of text

#include
#include
#include
#define N1 1
#define N2 200

void main()
{

int i,n,num,m=0,r,r1;
char str[80];
clrscr();

printf("\n\n\n\t\t Program for Encoding & Decoding a Line of text");


printf("\n\n\n\t\t\t Enter a line of text :");
printf("\n\t >> ");
gets(str);

printf("\n\n\n\t Encoding >> ");
r=rand();


for(i=0;str[i]!='\0';i++)
{
m=0;
num=str[i]+r;
if(num>N2)
{

n=num;
while(n>=N2)
{
m=m+N2;
n=n-N2;

}
str[i]=num-m+N1;

}
else
{
str[i]=num;
}


printf("%c",str[i]);
}

printf("\n\n\n\t Decoding >> ");


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

num=str[i];
if(num>r)
{
str[i]=num-r;
}

else
{
m=0;
r1=r;
num=num-N1;
while(r1>=N2)
{
m=m+N2;
r1=r1-N2;
}
num=num+m;
str[i]=num-r;
}

printf("%c",str[i]);

}


getch();

}