How to use a nested if else statements in a for loop in c

I'm having issues with my for statement. I'm trying to have a nested if else statement inside and I'm using pointers. I've tried everything and I've looked all over the internet. I've placed comments beside the lines with errors but if you see something else that's wrong please let me know. Thank you

#include <stdio.h>
#include <stdlib.h>
#define TRUE 1
#define FALSE 0

void getinput(double*xptr, int*nptr)
{
int flag;
    do
    {
      flag = TRUE;
      printf("What is the value of x and the number of terms:");
      scanf("%lf %i", xptr, nptr);
      if (*nptr <= 0)
      {
        printf("The number of terms must be positive\n");
        flag = FALSE;
      }
    }
    while(flag == FALSE);
}

double sinHyper(double *xptr, int *nptr) {
    int i;
    double sum;
    double ti;
    i = 0;
    ti = 0;
    for (i = 0; i < *nptr; i = i+1)// I'm getting a Warning: comparioson between pointer and integer
    {
        if (i == 0)
        {
            sum = xptr;
        } else {
            ti = 2*i+1;
            ti = ti*2*i;
            ti = (xptr*xptr)/ti;// I'm getting a error: invalid operands to binary * (have 'double*' and 'double*')
            sum = ti*sum;
        }
    }
    return (sum);
}

void main() {
   int n;
   double x;
   double sinhx;
   getinput(&x, &n);
   sinhx = sinHyper(&x, &n);
   printf("For an x of %.0f with %i terms the sinh(x) is %f", x, n, sinhx);
    return 0;
}