804. n的阶乘

https://www.acwing.com/problem/content/806/

#include <iostream>
using namespace std;int fact(int n)
{int a = 1;for (int i = 1; i <= n; i ++ ){a *= i;}return a;
}int main()
{int n;cin >> n;cout << fact(n) << endl;return 0;
}

 805. x和y的最大值

https://www.acwing.com/problem/content/807/

#include <iostream>
using namespace std;int max(int a,int b)
{if(a < b) return b;return a;
}int main()
{int a,b;cin >> a >> b;cout << max(a,b) << endl;return 0;
}

808. 最大公约数

https://www.acwing.com/activity/content/problem/content/1998/ 

#include <iostream>
#include <cmath>
using namespace std;int gcd(int a,int b)
{for (int i = min(a,b); i > 0; i -- ){if(a % i == 0 && b % i == 0) return i;} 
}int main()
{int a,b;cin >> a >> b;cout << gcd(a,b) << endl;return 0;
}

811. 交换数值

https://www.acwing.com/problem/content/813/ 

#include <iostream>
#include <cmath>
using namespace std;void swap(int &a,int &b)
{int temp = 0;temp = a;a = b;b = temp;
}int main()
{int a,b;cin >> a >> b;swap(a,b);cout << a << " " << b << endl;return 0;
}

 812. 打印数字

https://www.acwing.com/problem/content/814/

#include <iostream>
#include <cmath>
using namespace std;void printf(int st[],int b)
{for (int i = 0; i < b; i ++ )cout << st[i] << ' ';
}int main()
{int a,b;cin >> a >> b;int st[a] = {0};for (int i = 0; i < a; i ++ )cin >> st[i];printf(st,b);return 0;
}

813. 打印矩阵

https://www.acwing.com/problem/content/815/

#include <iostream>
using namespace std;
const int N = 100;
void printf2D(int st[][N], int a, int b)
{for (int i = 0; i < a; i ++ ){for (int j = 0; j < b; j ++ ){cout << st[i][j] << ' ';}cout << endl;}
}int main()
{int a,b;cin >> a >> b;int st[N][N] = {0};for (int i = 0; i < a; i ++ ){for (int j = 0; j < b; j ++ ){cin >> st[i][j];}}printf2D(st,a,b);return 0;
}

819. 递归求阶乘

https://www.acwing.com/problem/content/821/ 

#include <iostream>
using namespace std;int a;
int dfs(int a)
{if(a == 1) return 1;else return a*dfs(a-1);
}int main()
{cin >> a;cout << dfs(a) << endl;return 0;
}

 820. 递归求斐波那契数列

https://www.acwing.com/problem/content/description/822/

#include <iostream>
using namespace std;
int a;
int dfs(int n)
{if(n <= 2) return 1;else return dfs(n-1) + dfs(n-2);
}int main()
{cin >> a;cout << dfs(a) << endl;return 0;
}