Array subscript is not an integer ошибка

C11dr 6.5.2.1 Array subscripting … «One of the expressions shall have type ‘‘pointer to complete object type’’, the other expression shall have integer type, and the result has type ‘‘type’’.» …

With [], you get to do:

// pointer_type[integer_type]
float data[];
int n;
float total;
total = data[n];

// or the unconventional equivalent
// integer_type[pointer_type]
total = n[data];  // But let's leave that for another post

// Instead the OP did
// pointer_type[pointer_type]
// and received error: "Array subscript is not an integer"
float *p;
total = data[p];

The usage of float is not the issue here, but the usage of a pointer.

An integer type includes types int, unsigned, size_t, long, etc.

I think the OP wanted the following (or something like this)

float deviation(float data[], int n) {
  if (i <= 0) return 0;
  float data_average = average(data, n);
  float total = 0.0;  // don't forget to set to 0.0
  float *p = data;

  while (p < (data + n)) {
    total += (*p - data_average) * (*p - data_average);
    p++;
    }
  return sqrt(total / n);  // div by 0 averted
}

following this previous question Malloc Memory Corruption in C, now i have another problem.
I have the same code. Now I am trying to multiply the values contained in the arrays A * vc
and store in res. Then A is set to zero and i do a second multiplication with res and vc and i store the values in A. (A and Q are square matrices and mc and vc are N lines two columns matrices or arrays).
Here is my code :

    int jacobi_gpu(double A[], double Q[], 
           double tol, long int dim){
  int nrot, p, q, k, tid;
  double c, s;
  double *mc, *vc, *res;
  int i,kc;
  double vc1, vc2;

  mc   = (double *)malloc(2 * dim * sizeof(double));
  vc   = (double *)malloc(2 * dim * sizeof(double));
  vc   = (double *)malloc(dim * dim * sizeof(double));

  if( mc == NULL || vc == NULL){
    fprintf(stderr, "pb allocation matricren");
    exit(1);
  }

  nrot = 0;

  for(k = 0; k < dim - 1; k++){

    eye(mc, dim);
    eye(vc, dim);

    for(tid = 0; tid < floor(dim /2); tid++){
      p = (tid + k)%(dim - 1);
      if(tid != 0)
    q = (dim - tid + k - 1)%(dim - 1);
      else
    q = dim - 1;

      printf("p = %d | q = %dn", p, q);
      if(fabs(A[p + q*dim]) > tol){

    nrot++;
    symschur2(A, dim, p, q, &c, &s);


    mc[2*tid] = p;                                               vc[2 * tid] = c;
    mc[2*tid + 1] = q;                                           vc[2*tid + 1] = -s;
    mc[2*tid + 2*(dim - 2*tid) - 2] = p;                         vc[2*tid + 2*(dim - 2*tid)   - 2 ] = s;
    mc[2*tid + 2*(dim - 2*tid) - 1] = q;                         vc[2 * tid + 2*(dim - 2*tid) - 1 ] = c;



    }
    }

    for( i = 0; i< dim; i++){
      for(kc=0; kc < dim; kc++){
    if( kc < floor(dim/2)) {
      vc1 = vc[2*kc + i*dim];
      vc2 = vc[2*kc + 2*(dim - 2*kc) - 2];
    }else {
      vc1 = vc[2*kc+1 + i*dim];
      vc2 = vc[2*kc - 2*(dim - 2*kc) - 1];
    }
    res[kc + i*dim] = A[mc[2*kc] + i*dim]*vc1 + A[mc[2*kc + 1] + i*dim]*vc2;
      }
    }

    zero(A, dim);

    for( i = 0; i< dim; i++){
      for(kc=0; kc < dim; k++){
    if( k < floor(dim/2)){
      vc1 = vc[2*kc + i*dim];
      vc2 = vc[2*kc + 2*(dim - 2*kc) - 2];
    }else {
      vc1 = vc[2*kc+1 + i*dim];
      vc2 = vc[2*kc - 2*(dim - 2*kc) - 1];
    }
    A[kc + i*dim] = res[mc[2*kc] + i*dim]*vc1 + res[mc[2*kc + 1] + i*dim]*vc2;
      }
    }


    affiche(mc,dim,2,"Matrice creuse");
    affiche(vc,dim,2,"Valeur creuse");

  }

  free(mc);
  free(vc);
  free(res);
  return nrot;
}

When i try to compile, i have this error :

    jacobi_gpu.c: In function ‘jacobi_gpu’:
jacobi_gpu.c:103: error: array subscript is not an integer
jacobi_gpu.c:103: error: array subscript is not an integer
jacobi_gpu.c:118: error: array subscript is not an integer
jacobi_gpu.c:118: error: array subscript is not an integer
make: *** [jacobi_gpu.o] Erreur 1

The corresponding lines are where I store the results in res and A :

res[kc + i*dim] = A[mc[2*kc] + i*dim]*vc1 + A[mc[2*kc + 1] + i*dim]*vc2;

and

A[kc + i*dim] = res[mc[2*kc] + i*dim]*vc1 + res[mc[2*kc + 1] + i*dim]*vc2;

Can someone explain me what is this error and how can i correct it?
Thanks for your help.

1. 11-06-2012

   
   

   #1

   

   
   Registered User
   

   ---

   array subscript is not an integer
   

   im getting the error when compiling the code…

   Code:

   float array[20];
   int last;
   array[last[array]];
   how to get red of this

   ---

2. 11-06-2012

   
   

   #2

   

   
   SAMARAS
   

   

   ---

   You have

   Code:

   array[last[array]];

   In general,if you are sure you want something like this,imagine it with numbers and arrays.It would be something like this
   if you want to access the index described by the last element of the array.
   So maybe you want to say

   ---

3. 11-06-2012

   
   

   #3

   

   
   Registered User
   

   ---

   still the same error,i think may be its due to types of the integer variable and float arrays

   ---

4. 11-06-2012

   
   

   #4

   

   
   SAMARAS
   

   

   ---

   Have you initialized variable last? Can you please post the code you complied?

   ---

5. 11-06-2012

   
   

   #5

   

   
   Registered User
   

   ---

   im just checking the syntax errors
   i have initialised int last = n-1;
   int *l ;
   l = &last;

   ---

6. 11-06-2012

   
   

   #6

   

   
   SAMARAS
   

   

   ---

   What is n?Where is the array you were talking about?
   Just post all the code you have (i consider it is small from what you say )
   Also it would be very kind of you if you could wrap your code in code tags.It is easy
   [key]/*Your code here*/[/key] Replace key with code in order this to work.

   EDIT : it is ok to say

   Code:

   int a=5;
   int* p;
   p=&a;

   Last edited by std10093; 11-06-2012 at 05:17 AM.

   ---

7. 11-06-2012

   
   

   #7

   

   
   Registered User
   

   ---

   Originally Posted by prathiksa
   

   still the same error,i think may be its due to types of the integer variable and float arrays

   Yes it is.

   Arrays can only be indexed using values that have integral type (char, int, long, unsigned, etc). They cannot be indexed using non-integral values (float as in your case, struct types, etc).

   There is also an obscure corner of C that causes «array[index]» and «index[array]» to be equivalent (assuming array is (well….) an array or a pointer, and index has integral type). Because of that, your expression «array[last[array]]» is equivalent to «array[array[last]]» which attempts to use array[last] as an index. In your code, array[last] is of type float so is not a valid index. Hence the compiler error.

   Right 98% of the time, and don’t care about the other 3%.

   If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Buttercup, and read this, this, and this before posting again.

   ---

8. 11-06-2012

   
   

   #8

   

   
   SAMARAS
   

   

   ---

   What i thought you wanted to do

   Code:

   #include <stdio.h>
   
   int main( int argc, char *argv[])
   {
     float array[5];
     int last = 4;
     array[0]=1.2;
     array[1]=1.3;
     array[2]=1.4;
     array[3]=1.5;
     array[4]=1.9;
   
     printf("%fn",array[last]);
   
     return(0);
   }

   grumpy is more experienced,so he is sure to have it better in his mind

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9. 11-06-2012

   
   

   #9

   

   
   Algorithm Dissector
   

   

   ---

   You get rid of the error by fixing or removing the nonsense code.
   Explain what you really want to do and we’ll show you how to write code for it that makes sense.

   My homepage
   Advice: Take only as directed — If symptoms persist, please see your debugger

   Linus Torvalds: «But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong»

   ---