Where is the bug in my polynomial calculation code?

my aim is to compare the two different method to calculate a polynomial.. but if you run it on a mac (my computer is MacBook Air) you will find the two results are different... .but.... if you delete the "/* ... */" part OR delete the two "//" before "for ..." it works fine...

plus..it works fine on linux...

can anyone tell me why?..

here is my program:

#define MAX_NUM 10
#define TEST_TIME 1
#define test_type double

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

test_type normal_method(test_type *a, test_type x, int degree)
{
    test_type s = 0.0;
    test_type e = 1开发者_开发百科.0;

    for (int i = 0; i <= degree; i++) {
        s += a[i] * e;
        e *= x;
    }

    printf("%lf\n", s);

    return s;
}

test_type horner_method(test_type *a, test_type x, int degree)
{
    test_type s = a[degree];

    for (int i = degree - 1; i >= 0; i--) {
        s *= x;
        s += a[i];
    }

    printf("%lf\n", s);

    return s;
}

void generate_data(test_type *a, test_type *x, int degree)
{
    srand( time(NULL) );
    for (int i = 0; i <= degree; i++) {
        a[i] = (test_type)(rand() % MAX_NUM + 1) / (test_type)(rand() % MAX_NUM + 1);
        *x = (test_type)(rand() % MAX_NUM + 1) / (test_type)(rand() % MAX_NUM + 1);
    }

}

int main()
{
    const int degree = 10;
    test_type a[degree];
    test_type x;

    generate_data(a, &x, degree);

//Just by clear the /**/ below, the program will work fine....
/*    
    printf("x = %lf\n", x);
    for (int i = 0; i <= degree; i++) {
        printf("%lf\n", a[i]);
    }
*/
    clock_t begin, end;

//  Or clear the two // below, it will work fine too....

    begin = clock();
//    for (int i = 0; i < TEST_TIME; i++) 
        normal_method(a, x, degree);
    end = clock();
    printf("The normal method used %d clock times\n", end - begin);

    begin = clock();
//    for (int i = 0; i < TEST_TIME; i++)
        horner_method(a, x, degree);
    end = clock();
    printf("The horner method used %d clock times\n", end - begin);

    return 0;
}

You are accessing memory that is out of bounds of the array you create in main and use in the other functions. This happens in at least three places.

• The loop bounds in normal_method go from zero to ten:

  for (int i = 0; i <= degree; i++) {  // a[degree] is out of bounds
  

• On the first line of horner_method you are accessing memory that is out of bounds of your array:

  test_type s = a[degree];  // a[degree] is out of bounds
  

• The loop bounds in generate_data are incorrect the same way as in normal_method:

  for (int i = 0; i <= degree; i++) {  // a[degree] is out of bounds
  

You shouldn't use %lf to print a double. Just %f is fine. You probably confused that with scanf, which needs the l.

With the compiler warning options -Wall -Wextra -Wformat=2 gcc should tell you what's wrong in your code.