aa

int combine(char in[])
{
	
	int len;
	char *out;
	len= strlen(in);
	printf("<<<<<<<<Combinations>>>>>>");
	out=(char *)malloc(sizeof(char)*(len+1));
	if(!out)return -1;

	DoCombine(in,out,len,0,0);
	free(out);
	return 1;
}


void DoCombine(char *in, char *out, int len, int 
recLevel,int start)
{
	int i;
	for(i=start;i<len;i++)
	{
		out[recLevel]=in[i];
		out[recLevel+1]='\0';
		printf("\n%s\n",out);
		if(i<len-1)
			
DoCombine(in,out,len,recLevel+1,i+1);
	}
}

#include<stdio.h>
long pow(long a,long b)     /*finds a power of b*/
  {
long i,j=1;
for(i=1;i<=b;i++)
j*=a;
return j;
  }
long bin(int n)            /*converts into binary equivalent */
  {
long i=0,j=1,r;
while(n)
  {
r=n%2;
i=i+r*j;
n/=2;
j*=10;
  }
return i;
  }
  main()
  {
 char a[25];
 long i,j,k,m,l=0,n=0;
  printf("\nEnter string:");
 scanf("%s",a);
 printf("\nAll possible substrings are:\n");
 while(a[l])
 l++;
 printf("%d)\t{ }\n",++n);
  for(i=1;i<pow(2,l);i++)
 {  k=bin(i);
    m=l-1;
  printf("%d)\t{  ",++n);
  while(m>=0)
  {
    j=k/pow(10,m);
    if(j==1)
  printf("%c",a[l-1-m]);

    k=k%pow(10,m);
  m--;
  }
  printf("\t}\n");
  }
  return 0;
  }

#include<stdio.h>
#include<conio.h>
long pow(long a,long b)     /*finds a power of b*/
  {
long i,j=1;
for(i=1;i<=b;i++)
j*=a;
return j;
  }
long bin(int n)            /*converts into binary equivalent */
  {
long i=0,j=1,r;
while(n)
  {
r=n%2;
i=i+r*j;
n/=2;
j*=10;
  }
return i;
  }
  main()
  {
 char a[25];
 long i,j,k,m,l=0,n=0;
  printf("\nEnter string:");
 scanf("%s",a);
 printf("\nAll possible substrings are:\n");
 while(a[l])
 l++;
 printf("%d)\t{ }\n",++n);
  for(i=1;i<pow(2,l);i++)
 {  k=bin(i);
    m=l-1;
  printf("%d)\t{  ",++n);
  while(m>=0)
  {
    j=k/pow(10,m);
    if(j==1)
  printf("%c",a[l-1-m]);

    k=k%pow(10,m);
  m--;
  }
  printf("\t}\n");
  }
 getch();
  return 0;
  }

#include <iostream>
#include <string>
using namespace std;
#include<math.h>

int main(int argc, char* argv[])
{
	char input[100];

	cout<<"input a string:"<<endl;
	gets(input);
	cout<<input<<endl;
	int strLen = strlen(input);
	int count = pow(2.0,strLen);
	string *str = new string[count];
	int num=0;
	cout<<"{}"<<endl;
	for(int i=0;i<strLen;i++)
	{
		str[num] = str[num]+input[i];
		cout<<"{"<<str[num]<<"}"<<endl;
		num++;
		for(int j=0;j<i;j++)
		{
			str[num] = str[j]+','+input[i];
			cout<<"{"<<str[num]<<"}"<<endl;
			num++;
		}
	}
	
}

# include<stdio.h>
# include<conio.h>
# include<alloc.h>
# include<string.h>
# include<math.h>

int bin[16];
void genbin(int);

void main()
{
	clrscr();
	char *str;
	int i=0,len=0;
	str = (char*)malloc(100);
	printf("Input a no. :");
	scanf("%s",str);
	len = pow(2,strlen(str));
	for(i=0;i < len;i++)
	{
		genbin(i);
		for(int j=0;j < strlen(str);j++)
		{
			if(bin[j] == 1)
			printf("%c",str[j]);
		}
		printf("\n");
	}
	free(str);
	getch();
}
void genbin(int n)
{
	for(int i=0;i<8;i++)
	{
	   bin[i] = n%2;
	   n /= 2;
	}
}

Here is a trivial Java function to do this.  At least two 
of the above answers do not work at all...???  The binary 
solution seems to have some merit but why make it so 
difficult and problem frought???  I put in an element 
counter to verify the correct number of elements in the set 
upon print out.  Call the function below using the obvious 
form:

printSubsets("", "abc");

static int m_cElements = 1;
private static void printSubsets(String prefix, String str)
{
   if(str.equals(""))
      System.out.println((m_cElements++)+": {"+prefix+"}");
   else
   {
      printSubsets(prefix, str.substring(1));
      printSubsets(prefix+str.substring(0,1), str.substring
(1));
   }
}

find the no of bits required to represent the value n.i.e.
no of elements in the set.This can be done using following
algorithm.
int bin(int n)
{
  if(n==1)return 1;
return 1_n/2_1+1;
}
print(char c[12],int b)
{
    for(int i=0;i<b;i++)
       if(c[i]=='1')
         printf("%c",65+i);
}

combinations(int n)
{
    int b=bin(n);
    char c[12];
     for(int i=0;i<pow(2,b);i++)
     {
          for(int j=1;j<b;j++)
               if(i>>1)
                c[j-1]='1';
                else
                 c[j-1]='0';

     print(c,b);
}

i have written the program to find all the proper subsets,but it doesnt print them in order
ex:
{a,b,c}
it will print:
{}
{a}
{a,b}
{b}
{a,c}
so on
(not in order}
if u want it mail me(goodluck87@gmail.com)