Radix Sorting Algorithm in c [closed] - c

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I have been tried to write radix sort in c.when i run my code with the static array it works well. but when i am trying to take random inputs from file it gives me an "Segmentation fault" at run time.help Please just help to modify this code
here is my code:
#include <stdio.h>
#include <stdlib.h>
#include<math.h>
#include<string.h>
int getMax(int arr[], int n)
{
int mx = arr[0];
int i;
for (i = 1; i < n; i++)
if (arr[i] > mx)
mx = arr[i];
return mx;
}
void countSort(int arr[], int n, int exp,int base)
{
int output[n];
int i;
int count[base];
memset(count, 0, sizeof count);
for (i = 0; i < n; i++)
count[ (arr[i]/exp)%base]++;
for (i = 1; i < base; i++)
count[i] += count[i - 1];
for (i = n - 1; i >= 0; i--)
{
output[count[ (arr[i]/exp)%base ] - 1] = arr[i];
count[ (arr[i]/exp)%base ]--;
}
for (i = 0; i < n; i++)
arr[i] = output[i];
}
void radixsort(int arr[], int n,int base)
{
int m = getMax(arr, n);
int exp;
for (exp = 1; m/exp > 0; exp *= 10)
countSort(arr, n, exp , base);
}
void print(int arr[], int n)
{
int i;
for (i = 0; i < n; i++)
printf("%d ",arr[i]);
}
int main(int argc,int argv[])
{
int base=atoi(argv[1]);
int num,i;
FILE *fp1=fopen("myFile1.txt","r");
int arr[50];
while(fscanf(fp1,"%d",&num)==1)
{
arr[i]=num;
i++;
}
int n = sizeof(arr)/sizeof(arr[0]);
radixsort(arr, n ,base);
print(arr, n);
fclose(fp1);
return 0;
}

Answer 1

You are assuming that the compiler has set the initial value of i to 0. However, this is not guaranteed. While many compilers reset variables to 0, many others just leave the contents of memory set at whatever it happened to be at compile time or at load time. You need to initialize the value before using it.
Additionally, you do not test to ensure that you are not overrunning the arr buffer. For example consider what would happen to arr[] if you happen to open a file that has 51 entries. You would attempt to add an entry to arr[50] which overruns the buffer.
You need to initialize i to 0 and make sure to break out if i becomes too great.
The calculation of n is always 50 because arr is 50 ints. You should use i as the count of how many entries have been read in.
int main(int argc,int argv[])
{
int base=atoi(argv[1]);
// int num,i; // This is the line that causes the error
int num;
int i = 0; // This needs to be initialized before use.
FILE *fp1=fopen("myFile1.txt","r");
int arr[50];
// You need to ensure that i does not overrrun the buffer.
while(fscanf(fp1,"%d",&num)==1 && (i < 49))
{
arr[i]=num;
i++;
}
// Since i was defined before the while, it should have the correct count
// This calculation of n is wrong if fewer than a full buffer is read
int n = sizeof(arr)/sizeof(arr[0]);
radixsort(arr, n, base);
print(arr, n);
fclose(fp1);
return 0;
}