C++随机数生成器，不是随机的，但总是返回相同的数字

Hi-im正在查找RandNum，以生成2-10之间的数字，然后将该数字从15中去掉。

现在，每次执行程序时，从15(PerseusHealth)中减去的数字都是7。我该如何修复它，并使其随机？

void desertpath()
{
int scorpianchoice; //the option the player chooses.
int Maxhit = 10; //Max hit the scorpian can do
int Minhit = 2; //Min hit the scorpian can do
int randNum = rand()%(Maxhit + Minhit) + Minhit; 
int healthremaining = PerseusHealth - randNum; //health left in option1.

if(scorpianchoice == 1)
{
cout << "You run under the Scorpians Legs in hopes to escape " << endl;
cout << "You are hit by the scorpians Sting for " << randNum << " hp!";
cout << "You have " << healthremaining << "/15 HP Left!" << endl;
cout << "You escape the Scorpian but not without taking some damage" << endl;
}