Segmentation Fault

I get a segmentation fault when I run this program. I attempted debugging, and I think the problem is in my pointer B, but I don't know why. The fault comes in the function "loesen" as soon as B is used

Code:

#include <stdio.h>
int k=4;
int eingabe(int i, int j, int n, int k, double **A, double *B){
     
     A = malloc(k * sizeof(**A));
     for(i=0; i<k; i++)
                A[i]=malloc(k * sizeof(**A));
     printf("Geben Sie ein Oberematrix Reihweise ein\n");
     
     for(i=0; i<k; i++){
          for(j=i; j<k; j++){
               scanf("%lf", &A[i][j]);
               
          }
     }
     B = malloc(k * sizeof(*B));
     printf("Geben Sie Loesung Vektor ein\n");
     for(i=0; i<k; i++)
              scanf("%lf", &B[i]);
     return 0;
               
}
int ausgabe(int i, int k, double *X){
     for(i=0; i<k; i++)
              printf("%lf", X[i]);
     return 0;
}
int loesen(int i, int j, int k, int n, double det, double *X, double *B, double **A, double summe){
     X = malloc(k * sizeof(*X));
     summe = 0;
     n = k-1;
     X[n] = B[n] / A[n][n];
     for(i=0; i<k; i++){
              for(j=i+1; j<n; j++)
                         summe += A[i][j] * X[j];
              X[i] = (1/A[i][i])* (B[i]-summe);        
     }
     for(i=0; i<k; i++)
              det *= A[i][i];
     if(det==0)
              printf("Matrix ist Singulaer\n");
              
     return 0;
}
int main(){
    int i, j, n;
    double *X, *B, **A, summe, det;
    eingabe( i, j, n, k, A, B);
    loesen( i, j, k, n, det, X, B, A, summe);
    ausgabe( i, k, X);
    getch();
    return 0;
    
       
}

Both A and B will remain unchanged after the return from eingabe since they are local variables inside eingabe.

But I don't try to change A or B. I just want to access their storage locations to call up the values so that I can do calculations. I should still be able to access them, right?

Damn, it's been too many times I encountered this.
Read this.
And think carefully.

Code:

 
     A = malloc(k * sizeof(**A));
    //  you mean ?
     A = malloc(k * sizeof(*A) );

ok, so I thought about it carefully and I would like to see if what I think so far is right. The problem is that my functions are only editing a copy of the pointer, so when I try to do use the values in the memory locations, I never actually allocated a value to them.

In the link, the suggested solutions are as follows: either
1) split my "eingabe" function into 2 functions and return the location of the pointers(&A and &B)
or
2) make a pointer point to the memory locations of my vectors/matrix

Am I close?



To the code, I have used what I typed previously and it worked, so I don't konw why it wouldn't this time.

apparently trying to return A and B doesn't work like I thought it would. I just don't understand the whole pointer thing as well as I should. I don't want to waste your time with trying to explain it to me step by step.

If you want matrix, it's better to use struct.

Code:

typedef struct {
   int row,col;
   double **value;
} matrix;

If you still want prefer original approach,

Code:

int eingabe(int i, int j, int n, int k, double ***A, double **B){

You're not returning anything at all.
Just because you have a * in there doesn't make it magically return things.

Code:

void foo ( int a ) {
  a = 1;
}
int main ( ) {
  int b = 0;
  foo( b );
  // what is b now?
}

To make it work, you need a pointer to the variable, from the callers perspective.

Code:

void foo ( int *a ) {
  *a = 1;
}
int main ( ) {
  int b = 0;
  foo( &b );
  // what is b now?
}

Now in your case, this would become

Code:

void foo ( double ***a ) {
  // well you get the idea by now ;)
}
int main ( ) {
  double **b = 0;
  foo( &b );
}

Don't pass in variables that you don't read from before they are written to.
Take the simplest function here:

Code:

int ausgabe(int i, int k, double *X){
     for(i=0; i<k; i++)
              printf("%lf", X[i]);
     return 0;
}

The first things that happen with each variable are:
'i' is set to 0
'k' is read to compare it with 'i'
'X' is read and used to access an array
This indicates that 'i' is not meant to be a parameter to this function.

Also, don't return something if you don't ever intend to do anything with that value (except in main).
Lets correct these things:

Code:

void ausgabe(int k, double *X) {
    int i;
    for (i=0; i<k; i++)
        printf("%lf", X[i]);
}

Your other two functions have the same problems. Try fixing those the same way.