1. 用于接收传递值的变量被称为形参（参量parameter），传递给函数的值称为实参（参数argument）
2. 有多个参数时，调用函数时只需要用逗号将参数分开，若类型相同必须分别指定每个参数的类型

程序清单7.3 twoarg.cpp

一个接受两个参数的函数，表明在函数中修改形参的值不会影响调用程序中的数据。

#include<iostream>
void n_chars(char c, int n);
int main()
{
	using namespace std;
	int times;
	char ch;
	cout << "Enter a character: ";
	cin >> ch;
	while (ch != 'q')
	{
		cout << "Enter an integer: ";
		cin >> times;
		n_chars(ch, times);
		cout << "\nEnter another character or press the q-key to quit: ";
		cin >> ch;
	}
	cout << "times in main() is " << times << ".\n";
	cout << "Bye\n";
	return 0;
}
void n_chars(char c, int n)
{
	while (n-- > 0)
		std::cout << c;
}

程序清单7.4 lotto.cpp

#include<iostream>
long double probability(unsigned numbers, unsigned picks);
int main()
{
	using namespace std;
	double total, choices;
	cout << "Enter the total number of choices on the game card and\n"
		"the number of picks allowed:\n";
	while (cin >> total >> choices && choices <= total)
	{
		cout << "You have one chance in ";
		cout << probability(total, choices);
		cout << " of winning.\n";
		cout << "Next two numbers(q to quit): ";
	}

	cout << "bye\n";

	return 0;
}

long double probability(unsigned numbers, unsigned picks)
{
	long double result = 1.0;
	long double n;
	long double p;
	for (n = numbers, p = picks; p > 0; n--, p--)
		result *= n / p;
	return result;
}

在函数头中定义了形参，函数内部还定义了其他变量，作用域都在函数内部，形参与局部变量的区别在于，形参从main（）函数中得到实参的值，函数体内部的局部变量是从函数中得到自己的值。