Question

I am not a C programmer. I have just started reading K&R’s TCPL last week.
I have written this 42 line code in Java. I tried converting it to C, but it is giving me a segmentation fault.

Here is the Java version: http://codepaste.net/m8jz6m

My failed attempt to port it to C:

//Not working.
#include <stdlib.h>
#include <string.h>
 
void caesar ( const int SIDE )
{    
    int array [SIDE] [SIDE] ;

    for ( int number = 1; number <= SIDE * SIDE; ++ number )
        array [ getY ( number, SIDE ) ] [ getX ( number, SIDE ) ] = number ;

    for ( int Y = 0; Y < SIDE; ++ Y ) {
        for ( int X = 0; X < SIDE; ++ X)
            printf ( sprintf ("%%%dd" , strlen(itoa(SIDE*SIDE))), array [Y] [X] );
        printf ("\n");
    }
}
 
int getX ( const int number, const int SIDE )
{
    return SIDE == 1 ? 0 : number > 4 * SIDE - 4 ? 1 + getX ( number - 4 * SIDE + 4, SIDE - 2 ) : number >= 3 * SIDE - 2 ? 0 : number >= 2 * SIDE - 1 ? 3 * SIDE - 2 - number : number > SIDE ? SIDE - 1 : number - 1 ;
}
 
int getY ( const int number, const int SIDE )
{
    return SIDE == 1 ? 0 : number > 4 * SIDE - 4 ? 1 + getY ( number - 4 * SIDE + 4, SIDE - 2 ) : number >= 3 * SIDE - 2 ? 4 * SIDE - 3 - number : number  >= 2 * SIDE - 1 ? SIDE - 1 : number > SIDE ? number - SIDE : 0 ;
}
 
void main ( int argc, char *argv )
{
    if ( argc == 0 )
        printf ("\tUsage: java Caesar [side] | side:> Length and breadth of the square.\n");
    else
        caesar ( atoi( argv[1] ) );
}
 
 void itoa(int n, char s[])
 {
     int i, sign;

     if ((sign = n) < 0)  /* record sign */
         n = -n;          /* make n positive */
     i = 0;
     do {       /* generate digits in reverse order */
         s[i++] = n % 10 + '0';   /* get next digit */
     } while ((n /= 10) > 0);     /* delete it */
     if (sign < 0)
         s[i++] = '-';
     s[i] = '\0';
     reverse(s);
 }

  /* reverse:  reverse string s in place */
 void reverse(char s[])
 {
     int i, j;
     char c;

     for (i = 0, j = strlen(s)-1; i<j; i++, j--) {
         c = s[i];
         s[i] = s[j];
         s[j] = c;
     }
 }

Please let me know where I am going wrong.

Answer 1

• You are calling your itoa() function with one argument, while the function actually expects two.

• Also, it seems that this line:

  array [ getY ( number, SIDE ) ] [ getX ( number, SIDE ) ] = number ;
  

  could be better expressed with something like:

  array[number / SIDE][number % SIDE] = number;
  

  without using those getX and getY functions (that are curiously recursive). I haven’t examined those functions in detail to see what they actually do, but you may consider the above modification in any case.

• sprintf() is called with incorrect arguments. The first parameter should be the destination buffer. You seem to be using it as if it returned a string (it doesn’t).

• Look up the function of * inside a printf format specifier.