C- Fix Stack overflow in Recursion - c

Question

A code in C to find maximum of an array using divide and conquer but it keeps throwing
"stack overflow exception" . Help would be appreciated!
int a[10];
int find(int l,int h)
{
int x;
if(h==0)
{
x=0;
return x;
}
else
{
if(h==1)
{
if(a[0]>a[1])
{
x=0;
return x;
}
else
{
x=1;
return x;
}
}
else
{
int mid,z,y;
mid=(l+h)/2;
y=find(0,mid);
z=find(mid+1,h);
if(a[y]<a[z])
{
x=z;
}
else
{
x=y;
}
return x;
}
}
}
There are only limited variables and I don't see where the function can go into an infinite recursion.
int main()
{
int i,n,max,min,ans;
scanf("%d",&n);
for(i=0;i<n;i++)
{
scanf("%d",&a[i]);
}
ans=find(0,n-1);
printf("the maximum element is- %d\n",ans);
getch();
return 0;
}

Answer 1

Consider the case where you call find(0, 2). Since h > 1, you enter the second else clause, and mid is 1. Then on the second recursive call, it is to find(2, 2). On this recursive call, you again enter the second else, since h is still 2. But the mid is also 2. Now, the first recursive call goes to find(0, 2), which enters an infinite loop.
find(0, 2)
h not 0
h not 1
mid = 1
find(0, 1)
find(2, 2)
h not 0
h not 1
mid = 2
find (0, 2) <-- loop
It seems the intention of the if checks on h is to prevent the mid calculation from being the same as l. If so, then you can calculate the mid variable at the top of your function, and use that as the stopping condition.
It looks like this is an attempt to use divide and conquer to locate the position of the maximum element in the array a. If so, then your first recursive call should restrict itself to the range of [l..mid] instead of going back to 0.
Putting it all together:
int find(int l,int h)
{
int mid = (l+h)/2;
if (mid == l)
{
return (a[l] > a[h]) ? l : h;
}
else
{
int y = find(l, mid);
int z = find(mid+1, h);
return (a[y] > a[z]) ? y : z;
}
}

Answer 2

Here is your code modified, which is running successfully..
The problem is that you weren't checking the difference between l and h but only the value of h...
#include <iostream>
using namespace std;
int a[10];
int find(int l,int h)
{
int x;
if(h-l==0)
{
return h;
}
else
{
if(h-l==1)
{
if(a[l]>a[l+1])
{
return l;
}
else
{
return l+1;
}
}
else
{
int mid,z,y;
mid=(l+h)/2;
y=find(0,mid);
z=find(mid+1,h);
if(a[y]<a[z])
{
x=z;
}
else
{
x=y;
}
return x;
}}}
int main()
{
a[0]=3;
a[1]=7;
a[2]=5;
cout<<find(0,2)<<endl;
return 0;
}

Answer 3

you're using wrong conditions, try:
first if: if(h==l)
second if: if(h-l==1)
third if:
if(a[h]>a[l]) {
return h;
} else {
return l;
}