how to make a decrypt code for this encrypt program

Question

int encrypt (n)

int a=n/1000;
int b=(n/1000)/100;
int c=(n%100)/10;
int d=n%10;

a=(a+7)/10;
b=(b+7)/10;
c=(c+7)/10;
d=(d+7)/10;

return ((c*1000)+(d*100)+(a*10)+b);

Answer 1

Wouldn't you just reverse the math, using correct order of operations?

Answer 2

using manual computauin it will work but if i run that in my program it will not work .. the answer is always 0