what's wrong with it?

[Zhiyong Xu <rodgexu@xxxxxxxxx>]

t.c

/*
* Evaluate a function at three points, displaying
results.
*/
void
evaluate(double f(double f_arg), double pt1, double
pt2, double pt3)
{
      printf("f(%.5f) = %.5f\n", pt1, f(pt1));
      printf("f(%.5f) = %.5f\n", pt2, f(pt2));
      printf("f(%.5f) = %.5f\n", pt3, f(pt3));
}

compile:
$gcc -lm ex.c t.c
$./a.out
f(2.00000) = 0.90930
f(3.00000) = 0.14112
f(4.00000) = -0.75680
f(2.00000) = 1.41421
f(3.00000) = 1.73205
f(4.00000) = 2.00000

if change ex.c, add the prototype of function evaluate

ex.c

#include <stdio.h>
#include <math.h>

void
evaluate(double f(double f_arg), double pt1, double
pt2, double pt3);

int main(void)
{
        evaluate(sin, 2,3,4);
        evaluate(sqrt,2,3,4);

        return(0);
}

compile:
$gcc -lm ex.c t.c
$./a.out
f(2.00000) = 0.90930
f(3.00000) = 0.14112
f(4.00000) = -0.75680
f(2.00000) = 1.41421
f(3.00000) = 1.73205
f(4.00000) = 2.00000


here's the description:
1. I have a function evaluate defined in t.c
2. in ex.c, I call function evaluate without prototype
defined. 
using gcc -lm ex.c t.c, I can generate the executable
file a.out,
when executing, the result is wrong
3. if I modify ex.c, add the prototype definition, the
result is correct.

Anything wrong with the first case?


 
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