# 190. Function Evaluation

## I'm a slow walker, but I never walk backwards.

Write a function to evaluate $f(x, y) = 4 \ast x - 6 \ast y$ for a lot of $x$ and $y$. The prototype of the function is as follows.

1int evaluate_f(int *iptr[], int n, int *index);


Each pointer in iptr points to an array of two integers. The first integer is $x$, and the second integer is $y$. The length of the pointer array is $n$, so there are $n$ pairs of $x$ and $y$ that you need to evaluate $f(x, y)$. Compute these $f(x, y)$ and return the maximum as the return value of evaluate_f. Also you need to set index so that it becomes the index into iptr where the maximum happens. If the maximum value can be evaluated from multiple $(x, y)$ pairs, set the index to be the smallest among them. For example, if the $x$ and $y$ pointed by iptr and iptr both have the maximum $f(x, y) = 100$, then evaluate_f should return $100$ and index should be set to $3$. Variable $n$ is always positive.

n > 0

## Sample Input

We may test your program in the following code:

12345678910111213#include <stdio.h>#include "evaluate_f.h" int main(){  int a[] = { 9, 7 };  int b[] = { 3, 2 };  int c[] = { 3, 2 };  int d[] = { 9, 7 };  int *iptr[] = { a, b, c, d };  int max, index;  max = evaluate_f(iptr, 4, &index);  printf("%d %d\n", max, index);}


## Sample Output

0 1