type 自定義函數名(參數) {
  /* 你想做的事 */
  return 回傳變數;
}

#include <iostream>
using namespace std;
 
int f(int x){
	return 2*x+1;
}
int main(){
    cout << f(1) << endl;
    cout << f(5) << endl;
    cout << f(10000) << endl;
}

int minus(int a,int b){
    return a-b;
}
int num = minus(1,2);
cout<<num<<endl;
//num = -1

int divide(int a,int b){
    if(b==0){
        return -1;
    }
    return a/b;
}

int ???(int a,int b,int c){
    //你要做的事
    return x1,x2;
}

void im_lemonilemon_status() {
  cout << "lemon tested positive\n";
}

int min(int a, int b){
    if(a<b){
    	return a;
    }else{
    	return b;
    }
}

int gcd(int a, int b){
    if(a>b) swap(a, b);
    while(a!=b){
        if(a > b){
            a -= b;
    	} else{
            b -= a;
    	}
    }
    return a;
}

int gcd(int a, int b){
    if(a<b) swap(a,b);
    int tmp = 1;
    while(tmp != 0){
        tmp=a%b;
        a=b;
        b=tmp;
    }
    return a;
}

void swap(int &a, int &b){ 
    //&是參考，之後會學到
    int temp;
    temp = a;
    a = b;
    b = temp;
}