C, Compiler-Error and Pointers

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I'm having some trouble working with passing around arrays of floats. I throw some arrays of floats into the ActivationFunc, and then from there I throw those same arrays into the sgnFunction, which for some reason ends up having different values.

C

#include <stdio.h>
void sgnFunction(float *input[], float *weight[])
{
    printf("VALUES: %.2f %.2f %2.f, WEIGHTS: %.2f, %.2f, %.2f\n", *input[0], *input[1], *input[2], *weight[0], *weight[1], *weight[2]);
}

void ActivationFunc(float *x, float *w, float *n, int *d)
{
    printf("VALUES: %.2f %.2f %2.f, WEIGHTS: %.2f, %.2f, %.2f\n", x[0], x[1], x[2], w[0], w[1], w[2]);
    sgnFunction(&x, &w);
}

int main()
{
    float x1[3] = {1, 0, 1};
    float x2[3] = {0, -1, -1};
    float x3[3] = {-1, -0.5, -1};
    int d[3] = {0, 1, 1};
    float w[3] = {1, -1, 0};
    float n = 0.1;

    ActivationFunc(x1, w, &n, &d[0]);
}

If I remove the '&' from "sgnFunction(&x, &w);", I get a compiler error of:

test.c: In function 'ActivationFunc':
test.c:10:9: warning: passing argument 1 of 'sgnFunction' from incompatible pointer type
test.c:2:14: note: expected 'float **' but argument is of type 'float *'

Which I don't understand what it means to fix it. I know I'm probably just screwing something up with my use of pointers. A nice explanation of what's wrong, what I'm doing wrong with my pointers, and how to fix this would be greatly appreciated.

Posted 2-Oct-13 18:11pm

Shakurin

Updated 2-Oct-13 18:12pm

v2

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User 59241 · Accepted Answer · 2013-10-02T18:58:00

If you read this:

http://www.eskimo.com/~scs/cclass/notes/sx10f.html[^]

and this:

http://www.functionx.com/cpp/Lesson14.htm[^]

You will find this is how your code should read.

C++

#include <stdio.h>

void sgnFunction(float *input, float *weight)
{
    printf("VALUES: %.2f %.2f %2.f, WEIGHTS: %.2f, %.2f, %.2f\n", input[0], input[1],input[2],weight[0],weight[1],weight[2]);
}
 
void ActivationFunc(float *x, float *w, float *n, int *d)
{
    printf("VALUES: %.2f %.2f %2.f, WEIGHTS: %.2f, %.2f, %.2f\n", x[0], x[1], x[2], w[0], w[1], w[2]);
    sgnFunction(x, w);
}

int main()
{
    float x1[3] = {1, 0, 1};
    float x2[3] = {0, -1, -1};
    float x3[3] = {-1, -0.5, -1};
    int d[3] = {0, 1, 1};
    float w[3] = {1, -1, 0};
    float n = 0.1f;
 
    ActivationFunc(x1, w, &n, d);
}

Summary - When you pass an array to a function the compiler interprets it as a pointer. In sgnFunction you could even replace input[2] with *(input + 2).