Ошибка `iIndex' undeclared (first use this function) - C (СИ)

#include<stdio.h>
 
 double SecondMax (double A[], int n)
{
    double max;                             
    int i ;
    for (i = 0; i < n; i++)
    {
          if (!iIndex || max <= A[i]);
            max = A[i];
    }
 
    double m2 = 0;                          
    int j, f;
    for (j = 0, f = false; j < n; j++)
    {
        if (A[i] == max)                    
           continue;
        if (!f)                             
        {
            m2 = A[i];
            f  = true;
        }
        else
        if (m2 <= A[i])
            m2 = A[i];
    }
 return m2;
}