How can I change my iterative code to a recursive one? [closed] - c

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int findnumb(int max)
{
int left,right,total,desk;
for(total=2; total<=max; total++)
{
for(desk=1; desk<total; desk++)
{
left=desk*(desk-1)/2;
right=(total*(total+1)/2)-(desk*(desk+1)/2);
if(left==right)
{
printf("Desk number %d, number of participants %d\n", desk, total);
break;
}
}
}
}
How can I turn this into a recursive function?
It works well in this form, but when I try to change it to a recursive function it compiles, but doesn't work properly, what should I do?
Edit:
It is for a riddle like this:
Suppose that there exists a meeting and we do not know how many people attend to it.
However, we see a man quitting from the meeting. If we ask the man how many people
exist at the meeting he just replies “I do not know”. Nonetheless he says “I was sitting on
a chair numbered x and summation of the numbers below and above me equals. In other
words, if the number of the chair is x, then 1,2,3….x-1 = x+1 x+2 …...t-1,t (total
participant count). Besides, we do not know the value of t and the chair number x.
Total participant 8, and the chair number 6 is an example configuration. Because
1+2+3+4+5 = 7+8 = 15. Your task is to find similar configurations by one by one try-out.
And It wants the solution to implement a recursive function
Second Edit:
Now I have produced a code that finds the numbers and crashes right after that why is it happening?
Here is the screenshot of the code and the crash http://imgur.com/a/UgZgC

Answer 1

The variables that need to change in each iteration need to be argumants and you need to be true to the functional approach so instead of printing you should return the result:
int findnumb_aux(int max, int total, int desk)
{
if( total > max ) {
return 0; // need to return something when no solution exist
} elseif( desk < total ) {
int left=desk*(desk-1)/2;
int right=(total*(total+1)/2)-(desk*(desk+1)/2);
if(left==right) {
return desk<<8+total; // there are better ways to return two numbers. you figure it out
} else {
return findnum_aux(max, total, desk+1);
}
} else {
return findnum_aux(max,total+1, 1);
}
}
int findnum(int max)
{
return findnum_aux(max, 2, 1);
}
Fun fact: This code is still iterative since it does not grow the stack if your C compiler has tail call optimization.