#include <stdio.h>
int main() {
float a[]={2.0, 3.2, 1.2, -12.0, 1.5, 6.2};
float d[]={-1.0, 2.2, 4.1, 10.1, 1.0/5.0, 2.1};
float x,y;
printf ("vvedite x:\t");
scanf ("%f", &x);
y=d[0]+(x-a[0])*(d[1]+(x-a[1])*(d[2]+(x-a[2])*(d[3]+(x-a[3])*(d[4]+(x-a[4])*(d[5]+(x-a[5]))))));
printf ("%f\n", y);
return 0;
}

#include <stdio.h>
int main() {
float a[]={2.0, 3.2, 1.2, -12.0, 1.5, 6.2};
float d[]={-1.0, 2.2, 4.1, 10.1, 1.0/5.0, 2.1};
float x,y;
printf ("vvedite x:\t");
scanf ("%f", &x);
y=1;
for (int i=5; i>0;i--)
y=d[i]+(x-a[i])*y;
printf ("%f\n", y);
return 0;
}

for (int i=5; i>=0;i--)
...