What does fac mean in c++

The fac namespace in C contains the factorial function, which is used to calculate the factorial value of a non-negative integer. Its calculation method is recursive: fac(n) = n * fac(n-1), and returns 1 when n is 0. You can use the fac function directly in your code by including the "using namespace std;" directive.

fac in C

#fac in C is a namespace used to represent the factorial function. The factorial function computes the factorial value of a given nonnegative integer.

Factorial calculation

Factorial calculation uses recursion to calculate the factorial of a given non-negative integer n:

<code class="cpp">int fac(int n) {
  if (n == 0) {
    return 1;
  } else {
    return n * fac(n - 1);
  }
}</code>

Namespace usage

In order to use the fac namespace, you need to include the following instructions in the code:

<code class="cpp">using namespace std;</code>

After including this instruction, you can use the functions in the fac namespace directly in the code:

<code class="cpp">int result = fac(5); // 计算 5 的阶乘并存储在 result 中</code>

Example

The following code example shows how to calculate the factorial of 5 using the fac namespace:

<code class="cpp">#include <iostream>
using namespace std;

int main() {
  int n = 5;
  int result = fac(n);
  cout << "5 的阶乘为：" << result << endl;

  return 0;
}</code>

Output result:

<code>5 的阶乘为：120</code>

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