C语言如何实现一些算法或者函数你知道吗_C 语言

#include
using namespace std;
int fibonacci(int n){
	if(n == 1)return 1;
	else if(n == 2)return 1;
	else return fibonacci(n-1)+fibonacci(n-2);
	
}
int main(){
	int n;
	cin>>n;//返回斐波那契数列第几项 
	cout<

#include
using namespace std;
int a[20], b[20];//a[]为排列的盒子，b[]为判断元素是否放过的数组 
int n;
void perm(int k){//k表示开始放第k个数 
	if(k == n+1){//当k>n时说明第k个数已经放好，已经一组排列完毕 
		for(int i=1; i<=n; i++){
			cout<>n;//排列数个数 
	perm(1);//从放第一个数开始排列 
	return 0;
} 

#include
using namespace std;
int gcd(int a, int b){
	return b==0?a:gcd(b, b%a);
} 
int main(){
	int a, b;
	cin>>a>>b;
	cout<

#include
using namespace std;
long mul(long x, long y, long n){
	if(x == 0 || y == 0)return 0;
	else if(n == 1)return x * y;
	else{
		long A = (long)x / pow(10, (long)(n/2));
		long B = x - A * pow(10, n/2);
		long C = (long)y / pow(10, (long)(n/2));
		long D = y - C * pow(10, n/2);
		long AC = mul(A, C, n/2);
		long BD = mul(B, D, n/2);
		long A_BD_C = mul((A - B),(D - C), n/2); 
		return AC * pow(10, n) + (A_BD_C + AC + BD)* pow(10, (long)(n/2)) + BD;
	}
}
int main(){
	long a, b, n, sign;
	if((a<0 && b>0) || (a>0 && b<0))sign = -1;
	else sign = 1;
	cin>>a>>b>>n;
	cout<