Bubble Sort ending in an infinite loop - c

Question

I created a program for bubble sort. It ends up in an infinite loop.
I have included comments at places so that the code is easily understandable.
Any suggestions on how to make the code smaller are welcome.
I was debugging the program and found this -
When stdin was "ccbbaa" and after some recursions when finally input(aabbcc) and temp(aabbcc) were same, then after the condition of strcmp() was executed, the value of 'temp' was changed to "baabcc".
Any reasons as to why this happened? — This is the reason for the infinite loop.
Does a character array have a '\0' at the end (while copying input to temp)?
I solved the problem by using a for loop instead of strcmp(). Investigating why strcmp() doesn't work currently.
Updated code is available - http://ideone.com/4Bdblh ( solved )
Buggy code
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
#include<ctype.h>
void sort(char* input)
{
const int length = strlen(input);
int j = length -1;
char temp[length];
for(int i=0; i<length; i++)
{
temp[i]= *(input+i);
}
while(j)
{
if((int)*(input+1) < (int)*(input))
{
char temp1;
temp1 = *(input);
*input = *(input + 1);
*(input + 1) = temp1;
}
input++;
j--;
}
input = input - length +1;
while(strcmp(temp,input))
{
sort(input);
}
}
int main()
{
char* input = malloc(sizeof(char)*1000);
scanf("%[^\n]%*c",input);
sort(input);
printf("%s",input);
return 0;
}

Answer 1

Answer using arrays and for loops-
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
#include<ctype.h>
#define MAX 1000
void sort(char input[])
{
const int length = strlen(input);
int j = length -1;
char temp[length];
for(int i=0; i<length; i++)
{
temp[i]= input[i];
}
int l=0;
while(j)
{
if(input[l+1] < input[l])
{
char temp1;
temp1 = input[l];
input[l] = input[l+1];
input[l+1] = temp1;
}
l++;
j--;
}
for(int k=0; k<length; k++)
{
if(temp[k]!=input[k])
{
sort(input);
}
}
}
int main()
{
char input[MAX];
scanf("%[^\n]%*c",input);
sort(input);
printf("%s",input);
return 0;
}

Answer 2

In C a string is just a char array ending in 0.
All string functions assume char arrays end with zero.
strcpy copies the string including the 0 delimiter at the end. Therefore, destination must have enough space for the string plus the zero.
strlen returns the length of the string, so the destination must be at least strlen (input)+1 long.
If you copy the string in a loop, then you mustn't forget to add the ending zero.
What I don't really get is why to make it recursive and doing a string comparison to detect completion. You can just implement two nested loops from 0 to length - 2. It's warranted it'll be sorted in the end.
If you want to make it adaptive, just store the last position you swapped. You needn't go further the next loop.

Answer 3

When stdin was "ccbbaa" and after some recursions when finally input(aabbcc) and temp(aabbcc) were same, then after the condition of strcmp() was executed, the value of 'temp' was changed to "baabcc".
Any reasons as to why this happened? — This is the reason for the infinite loop.
It just looked like the value of 'temp' was changed to "baabcc" because the function returned to the previous recursion level where the local temp had the same value as before. The main reason for the infinite loop is that due to the while(strcmp(temp,input)) the old, unsorted temp is compared again and again.
Does a character array have a '\0' at the end (while copying input to temp)?
The temp array in the buggy code hasn't; you could have written
char temp[length+1];
strcpy(temp, input);
or just used strncmp() rather than strcmp().
So, for the program to work it is sufficient to change
while(strcmp(temp,input))
to
if (strncmp(temp, input, length))