Determination of polynomials - arrays

Question

I need help solving this task, if anyone had a similar problem it would help me a lot.
The task is:
Write a program that calculates the degree and polynomial p(x) for a given x.
For example:
Enter n:2 //degree of polynomial and function degree
Enter x:2
x^n=4
Enter coefficients of polynomial:
a[0]=1
a[1]=2
a[2]=3
P(x)=3*x^2 + 2*x^1 +1*x^0 = 17
I did it like this:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define MAX 100
/*
*/
typedef struct polynomial {
double coef[MAX];
} POLYNOMIAL;
double degree(double ,int );
double px(POLYNOMIAL ,double );
int main()
{
POLYNOMIAL p;
double x,pom;
int n;
printf("Enter degree (n>=0):");
scanf("%d",&n);
while(n<1 || n>MAX)
{
printf("Enter degree (n>=0):");
scanf("%d",&n);
}
printf("Enter x:");
scanf("%lf",&x);
pom=degree(x,n);
printf("%.2lf^%d =%lf",x,n,pom);
printf("\nEnter coefficients of polynomial :\n");
for(int i=0;i<=n;i++)
{
printf("a[%d]:",i);
scanf("%lf",&p.coef[i]);
}
return 0;
}
double degree(double x,int n)
{
double degree=1;
if(n==0)
{
return 1;
}
for(int i=1;i<=n;i++)
{
degree*=x;
}
return degree;
}
double px(POLYNOMIAL p,double x)
{
double sum=0;
for(int j=0;j<"I don't know what to put here";j++)
{
sum+=(double)p.coef[j]*degree(x,j);
}
printf("%lf",sum);
}
The problem arises when calculating polynomials, because I don't know what to put as a condition in the for loop, there should be j < of the length of the array entered, that is, of degree n,
but n cannot be used as a parameter in the px function? The task must be done with the structure and functions listed.
Thanks in advance !

Answer 1

If you are not allowed to pass n to the function, you can instead just loop to MAX and make sure that all unused coefficients are zero.
In other words, just initialize all elements of p to zero
POLYNOMIAL p = {.coef = {0} };
and let the loop be:
j < MAX
BTW: Notice that you need return sum in the function.
Further the function degree is pretty unnecessary. Consider this:
double px(POLYNOMIAL p,double x)
{
double sum=p.coef[0];
double d = x;
for(int j=1;j<MAX;j++)
{
sum+=(double)p.coef[j]*d;
d = d * x;
}
printf("%lf",sum);
return sum;
}