Combination of letters

// List all combinations of letters in a string. Suppose no letter is repeated.
// traverse letters from the first one to the last one.
// combination[ ] is used to save the result of each combination.
// layer indicates the number of letters in the combination, also it tells you
// the position of the newly visited letter in combination[ ]
// layer increases by one in each recursion



Algorithm:

C(string, combination, length, layer, start)

for i = start to length
    // put the traversed letters into combination[]
    combination[layer] = string[i]
    print the combination
    if (start+1 <= length) C(string, combination, length, layer+1, i+1)

Code:

#include
#include

using namespace std;


int sum =0;

char str[] = "1234";

int length;

char *combination;



void DoCombine(char in[], char combination[], 
              int length, int layer, int start)

{

    int i;

    for( i = start; i < length; i++)
    {
        combination[layer] = in[i];
        combination[layer+1] = 0;
        cout << combination << endl;
        if(i < length - 1)
            DoCombine(in, combination, 
                      length, layer+1, i+1);
    }
}


int main()
{
    length = strlen(str);
    combination =  new char[length+1];
    DoCombine(str, combination, length, 0, 0);
    delete [] combination;

    return 0;
}