(C) Radix Sort array from text file - c

Question

I am attempting to get this queue-based radix sort to work, but I can't seem to figure out what's wrong with it. It uses a text file as the input medium and throws tons of errors when I try to compile it and run it with the text file.
Any advice would be helpful at this point.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAX 10
#define SHOWPASS
//Compiled Using GNU GCC Compiler
void radixsort(int *a[], int n)
{
int i, b[MAX], m = *a[0], exp = 1;
for (i = 0; i < n; i++)
{
if (*a[i] > m)
m = a[i];
}
while (m / exp > 0)
{
int queue[10] =
{ 0 };
for (i = 0; i < n; i++)
queue[*a[i] / exp % 10]++;
for (i = 1; i < 10; i++)
queue[i] += queue[i - 1];
for (i = n - 1; i >= 0; i--)
b[--queue[*a[i] / exp % 10]] = *a[i];
for (i = 0; i < n; i++)
*a[i] = b[i];
exp *= 10;
#ifdef SHOWPASS
printf("\nPASS : ");
radixsort(a, n);
#endif
}
}
int main( int argc, char *argv[] )
{
if ( argc != 3 )
{
printf("Need two input parameters in the following order: \n 1. Input file path \n 2. Number of elements in file\n");
return 0;
}
int num_elements = atoi(argv[2]);
int *input_arr = (int*) calloc (num_elements, sizeof(int));
int i;
FILE *fin; //File pointer to read input file
fin = fopen(argv[1], "r"); //Initialize file pointer
for(i=0; i<num_elements; i++)
{
fscanf(fin, "%d", &(input_arr[0]));
}
radixsort(input_arr[0], i);
printf ( "\nArray before sorting: \n") ;
for ( i = 0 ; i < num_elements ; i++ )
printf ( "%d\t", input_arr[0] ) ;
printf ( "\n\n");
return 0;enter code here
}

Answer 1

There are plenty of errors in your code. Firstly, the way you are taking input is incorrect.
fscanf(fin, "%d", &(input_arr[0]));
While taking input, the array input_arr is filled with a single input value at input_arr[0]. The rest of the input is over-written at input_arr[0].
Replace it with, fscanf(fin, "%d", &(input_arr[i]));.
Even you are displaying output in incorrect way.After sorting, the same output will be displayed num_elements times because of the following incorrect statement:
printf ( "%d\t", input_arr[0] ) ;
Again replace the above statement with printf ( "%d\t", input_arr[i] ).
As an impact of following incorrect statement,
fscanf(fin, "%d", &(input_arr[i])); ,
your program experiences a Segmentation fault, since in function radixsort, you are iterating from 0 to n-1(Number of elements).
for (i = 0; i < n; i++)
{
if (*a[i] > m)
m = a[i];
}
As only a[0] is filled with input value and rest of the array(from a[1] to a[n-1]) contains a garbage value, you will get a runtime error while executing your code.
There are lot of other bugs too, which i had fixed. This is the perfect running code:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAX 10
// #define SHOWPASS
// Compiled Using GNU GCC Compiler
void radixsort(int a[], int n)
{
int i, b[MAX], m = a[0], exp = 1;
for (i = 0; i < n; i++)
{
if (a[i] > m)
m = a[i];
}
while (m / exp > 0)
{
int queue[10] = { 0 };
for (i = 0; i < n; i++)
queue[a[i] / exp % 10]++;
for (i = 1; i < 10; i++)
queue[i] += queue[i - 1];
for (i = n - 1; i >= 0; i--)
b[--queue[a[i] / exp % 10]] = a[i];
for (i = 0; i < n; i++)
a[i] = b[i];
exp *= 10;
#ifdef SHOWPASS
printf("\nPASS : ");
radixsort(a, n);
#endif
}
}
int main(int argc, char *argv[])
{
if (argc != 3)
{
printf
("Need two input parameters in the following order: \n 1. Input file path \n 2. Number of elements in file\n");
return 0;
}
int num_elements = atoi(argv[2]);
int *input_arr = (int *)calloc(num_elements, sizeof(int));
int i;
FILE *fin; // File pointer to read input file
fin = fopen(argv[1], "r"); // Initialize file pointer
for (i = 0; i < num_elements; i++)
{
fscanf(fin, "%d", &(input_arr[i]));
}
radixsort(input_arr, i);
printf("\nArray before sorting: \n");
for (i = 0; i < num_elements; i++)
printf("%d\t", input_arr[i]);
printf("\n\n");
return 0;
}