can u help? what is wrong with this????

void fibonacciModified(double t1, double t2, double n) { int i; double arr[20]; arr[0]=t1; arr[1]=t2; for(i=2;i<20;i++) { arr[i]=t1+t2*t2; t1=t2; t2=arr[i]; } for(i=0;i<20;i++) { if((i+1)==n) printf("%0.lf",arr[i]); } }