Any particular language? Here's one implementation in Java paraphrased from Robert Sedgewicks data structure's book:
Code:
static void quicksort(ITEM[] a, int l, int r) 
{   Stack S = new Stack(50); 
    S.push(l); S.push(r); 
    
    while (!S.empty())
    { 
        r = S.pop(); l = S.pop(); 
        
        if (r <= l) continue; 
        
        int i = partition(a, l, r); 
        
        if (i-l > r-i) { S.push(l); S.push(i-1); } 
        
        S.push(i+1); S.push(r); 
        
        if (r-i >= i-l) { S.push(l); S.push(i-1); } 
    } 
}