Ошибка c4700 использована неинициализированная локальная переменная

When I compile this code it says «error C4700: uninitialized local variable ‘b’ used». I’m not sure what I have to do now to fix this problem. I’m neither an IT student or technican but I very like to learn C++ and I’m learning it by myself. I’ve been on this for 1 day.

Many thanks

#include <stdio.h>
#include <iostream>

//A. 
//1--
void InputArray(int *a, int &n)
{
    printf("Insert n = ");
    scanf("%d", &n);
    a = new int[n];
    for (int i=0; i<n; i++)
    {
        printf("Enter the key's a[%d] values: ", i);
        scanf("%d",&a[i]);
    }
}


void main()
{
    int *b, m;
    InputArray(b, m);
}

I have a question related to my C/C++ code. I tried some researches but there was no specific answer for my problem. I hope you will response to my question as soon as possible.

Here is my full code in C language:

 #include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;
#define M 500
#define N 500
int
main ()
{
  //set number of threads here
  //omp_set_num_threads(8);
  int i, j, k;
  double sum;
  double **A, **B, **C;

  A = malloc (M * sizeof (double *));
  B = malloc (M * sizeof (double *));
  C = malloc (M * sizeof (double *));
  for (i = 0; i < M; i++)
    {
      A[i] = malloc (N * sizeof (double));
      B[i] = malloc (N * sizeof (double));
      C[i] = malloc (N * sizeof (double));
    }
  double start, end;
  for (i = 0; i < M; i++)
    {
      for (j = 0; j < N; j++)
        {
          A[i][j] = j * 1;
          B[i][j] = i * j + 2;
          C[i][j] = j - i * 2;
        }
    }
  start = omp_get_wtime ();
  for (i = 0; i < M; i++)
    {
      for (j = 0; j < N; j++)
        {
          sum = 0;
          for (k = 0; k < M; k++)
            {

              sum += A[i][k] * B[k][j];
            }
          C[i][j] = sum;
        }
    }

  end = omp_get_wtime ();
  printf ("Time of computation: %fn", end - start);

  cin.get ();
  return 0;
}

The code terminates because of some bugs.
The result of the code is given here:

error C4700: uninitialized local variable 'A' used

error C4700: uninitialized local variable 'B' used

error C4700: uninitialized local variable 'C' used

Please consider my question

Best Regards.

malloc() returns a void pointer, you have to cast it:

  A = (double**) malloc (M * sizeof (double *));
  B = (double**) malloc (M * sizeof (double *));
  C = (double**) malloc (M * sizeof (double *));
  for (i = 0; i < M; i++)
    {
      A[i] = (double*) malloc (N * sizeof (double));
      B[i] = (double*) malloc (N * sizeof (double));
      C[i] = (double*) malloc (N * sizeof (double));
    }

if you are using c++ maybe is better to use «new» instead of malloc:

  A = new double* [M];
  B = new double* [M];
  C = new double* [M];
  for (i = 0; i < M; i++)
    {
      A[i] = new double[N];
      B[i] = new double[N];
      C[i] = new double[N];
    }

answered Jan 11, 2015 at 21:11