Thread: Segmentation fault

Can anyone check ths code and tell me whats wrong? Im getting a Segmentation fault [COREDUMP] when im runnig my program. I do not get any error when compiling.

Code:

#include <stdio.h>
int size(void)
{
    int n; //size of matrix        
    printf ("What is the size of the matrix?"); //user input
    scanf ("%d",&n);
    return n;  
}
int recursion (int row, int column, int n) //Recursive function
{
    int result;
     
    result = ((row + 1) + column) % n;
    
    // If the result is 0, n will be returned. n is the last digit in the   
        series
    if (result == 0) 
    {
        return n;
    }
    else
    {
        return result;
    }
}
int main ()
{

    int row; //row of the matrix
    int column; // column of the matrix
    int n; // n is the size of the matrix as mentioned in the question 
    int square[n][n];
    
    n = size();
   
    for (row = 0; row < n; row++)
    {
         printf("\n");

         for (column = 0; column < n; column++)
         {
              square[row][column] = recursion(row, column, n);
              printf("%d", square);   // Prints the Result         
         }     
    }
    return 0;
}

In the program, I have to build a Latin square for n elements.
Eg of latin square for n=3;

1 2 3
2 3 1
3 1 2

I also get a warning, no new line at end of file.
What does that mean?

Code:

#include <stdio.h>
int size(void)
{
    int n; //size of matrix        
    printf ("What is the size of the matrix?"); //user input
    scanf ("%d",&n);
    return n;  
}
int recursion (int row, int column, int n) //Recursive function
{
    int result;
     
    result = ((row + 1) + column) % n;
    
    // If the result is 0, n will be returned. n is the last digit in the   
    /*What a heck is series?*/ 
		//   series
    if (result == 0) 
    {
        return n;
    }
    else
    {
        return result;
    }
}
int main ()
{

    int row; //row of the matrix
    int column; // column of the matrix
    int n; // n is the size of the matrix as mentioned in the question 
    int square[n][n];//this is invalid!
    
    //n = size();this makes no sence
   //you need something like
	 /*
		* int *foo = calloc(n,sizeof(int*));
		* foo[i] = calloc(n,sizeof(int));
		*/
    for (row = 0; row < n; row++)
    {
         printf("\n");

         for (column = 0; column < n; column++)
         {
              square[row][column] = recursion(row, column, n);
              //This is wrong you can't print the whole matrix at once
							printf("%d",square[?][?]);   // Prints the Result         
         }     
    }
    return 0;
}

This is the change I made. I still get the Segmentation Fault error as well as no new line at end of file warning. Please check.

Code:

#include <stdio.h>
int asksize(void)
{
    int n; //size of matrix        
    printf ("What is the size of the matrix?"); //user input
    scanf ("%d",&n);
    return n;  
}
int recursion (int row, int column, int n) //Recursive function
{
    int result;
     
    result = ((row + 1) + column) % n;
    
    // If the result is 0, n will be returned. n is the last digit in the   
        series// Series means from 1 to 10, 10 is the last digit. So if a user inputs the size. the square generates from 1 to n, where n is the last digit.
    if (result == 0) 
    {
        return n;
    }
    else
    {
        return result;
    }
}
int main ()
{

    int row; //row of the matrix
    int column; // column of the matrix
    int n; // n is the size of the matrix as mentioned in the question 
    int square[n][n]; //What is wrong with this declaration, as  
                                the  user will be giving the size of the array
    
    n = asksize();
   
    for (row = 0; row < n; row++)
    {
         printf("\n");

         for (column = 0; column < n; column++)
         {
              square[row][column] = recursion(row, column, n);
              printf("%d", square[row][matrix]);   // Prints the Result         
         }     
    }
    putchar('\n');
    return 0;
}

Im a beginner in C. So that seems like a recursive function to me. Aint it?

Hi Ron

The problem is with your array. square[n][n] is not accepted in C.

I have modified your main function which now uses dynamic allocation of two dimentional array.

Compile this code and it should work for you.

------------------------------------------------

Code:

#include <stdio.h>

int size(void)
{
    int n; /* size of matrix */
    printf ("What is the size of the matrix: "); /* user input */
    scanf ("%d",&n);
    return n;
}


int recursion( int row,  int column,  int n) /* Recursive function */
{
    int result;

    result = ((row + 1) + column) % n;

    /* If the result is 0, n will be returned. n is the last digit in the  series */
    if (result == 0)
    {
        return n;
    }
    else
    {
        return result;
    }
}


int main( )
{

    int row; /* row of the matrix */
    int column; /*  column of the matrix */
    int n; /*  n is the size of the matrix as mentioned in the question  */
    int **square; 

    n = size();

    /* Memory allocation for the matrix.... */
    square = (int **) malloc( n * sizeof(int));

    for (row = 0; row < n; row++)
    {
         for (column = 0; column < n; column++)
         {
              square[row] = (int *) malloc( n * sizeof(int));
         }
    }

    for (row = 0; row < n; row++)
    {
         printf("\n");

         for (column = 0; column < n; column++)
         {
              square[row][column] = recursion(row, column, n);
              printf("%d ", square[row][column]);   /* Prints the Result */
         }
    }
    printf("\n\n");

    free(square);

    return 0;
}

Regards
Ravi O. Rattihalli
[email protected]

Hi Ron

Further to my previous message.....

There is no need to have two for loops while allocationg memory!!
I saw that I have used two loops just now...

so it should be like this:

Code:

    /* Memory allocation .... */
    square = (int **) malloc( n * sizeof(int));

    for (row = 0; row < n; row++)
    {
        square[row] = (int *) malloc( n * sizeof(int));
    }

then the other for loop follows....


Cheers

Ravi O. Rattihalli

Yup.... I am aware of the warning :

Operation between types "int**" and "int" is not allowed..

But then how will you avoid that warning?? without casting it?

In such cases the documentation helps the developer whenever the declaration type is changed... so that he will change the cast accordingly... ( at the time of maintenance )

But the idea of using "sizeof *p" in malloc is very good.

If you know any best way of using malloc without cast and still avoid warnings, please let me know..

BTW, I had given the solution to Ron's problme so that he can atleast get rid of the segmentation fault and see the latin square :-)

Regards
Ravi

Hi Salem....

I guess you are right.. Need not cast the malloc if I use stdlib.h

and "itsme86" , thanX for the suggestion.. but saw ur mail after I corrected my code ;-) but I must thank you too.....

so Ron !!

here is your changed main again

Code:

int main(void)
{

    int row; /* row of the matrix */
    int column; /*  column of the matrix */
    int n; /*  n is the size of the matrix as mentioned in the   question  */

    n = size();
    int **square;

    /* Memory allocation for the matrix.... */
    square = malloc( n * sizeof(**square));
    for (row = 0; row < n; row++)
    {
        square[row] = malloc( n * sizeof(**square));
    }

    for (row = 0; row < n; row++)
    {
         printf("\n");

         for (column = 0; column < n; column++)
         {
              square[row][column] = recursion(row, column, n);
              printf("%d ", square[row][column]);   /* Prints the Result */
         }
    }
    printf("\n\n");

    free(square);

    return 0;
}

Regards
Ravi