zziz

std::string to_str(int num){
	std::string str = "";

	std::string nums[10];
	nums[0] = "0";	nums[1] = "1";	nums[2] = "2";	nums[3] = "3";	nums[4] = "4";
	nums[5] = "5";	nums[6] = "6";	nums[7] = "7";	nums[8] = "8";	nums[9] = "9";

	if(num == 0)	return nums[0];
	int d = pow(10, 1.0 + floor(log10(num)));
	while (d /= 10)	str += nums[(num / d) % 10];

zziz

print("Dave have {} pens.".format(5))

Dave have 5 pens.

zziz

double floor(double x){
	return (x >= 0) ? (int) x : (x == (int) x ? x : (int) x - 1);
}

double ceil(double x){
	return (x >= 0) ? ((x == (int) x) ? (int) x : (int) x + 1) : ((x == (int) x) ? (int) x + 1 : (int) x);
}

zziz

// Pre-order traversal
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */