invalid type argument of 'unary *' (have 'int')

Question

I have this C program:

#include <stdio.h>
#include <math.h>
main() {
  int I;
  double A[3]={0.0, 1.0, 2.0};
  double B[3]={0.0, 1.0, 2.0};
  double C[3]={0.0, 1.0, 2.0};
  double X[3];

  for (I=0; I<3; I++) {
      X[I] = A[I] * ( B[I] - C[I] )**2;
  }
}

compiling produces an error:

invalid type argument of 'unary *' (have 'int')

How should I fix this?

Also, take a look at https://stackoverflow.com/questions/2108192/what-are-the-valid-signatures-for-cs-main-function or even better, read a _good_ C book. I think you need one :) — hellow, Oct 08 '18 at 12:00
In some languages the `**` is to indicate an exponent. C is not one of these. — Jongware, Oct 08 '18 at 12:00
By the way, it would really really really help (more) if you provide as much additional information as you can. I bet the compiler also gave a specific line number. In this case, anyone with a `c` badge spotted the error from a mile away, but don't count on this. — Jongware, Oct 08 '18 at 12:03

Blaze · Accepted Answer · 2018-10-08T12:07:16.683

0

Here you are presumably trying to square an expression.

X[I] = A[I] * ( B[I] - C[I] )**2;

Do it like this instead:

X[I] = A[I] * pow(B[I] - C[I], 2.0);

I don't think there's an integer pow in math.h, but this answer provides a nice implementation.

edited Oct 08 '18 at 12:07

answered Oct 08 '18 at 12:00

Blaze

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Integer `pow` is of no relevance to the `double B[3]`and `double C[3]`. – Eric Postpischil Oct 08 '18 at 13:20
That would be a heterogeneous integer-floating-point `pow`, not an integer `pow`, and the link you give is for a pure integer `pow`. A `pow(double, int)` could be useful for some limited cases, but a good compiler will optimize `pow(x, 2)` to `x*x` anyway. – Eric Postpischil Oct 08 '18 at 13:25
Right, sorry. That's what I had in mind - and linked the wrong one anyway. I'd assume it's a simple modificiation to the int, int one however. :) – Blaze Oct 08 '18 at 13:27

invalid type argument of 'unary *' (have 'int')

1 Answers1