int fact(int val);

#include "fact.h"
int fact(int val)
{
    if (val == 1)
        return 1;
    return val * fact(val - 1);
}

#include <iostream>
#include "fact.h"
using namespace std;
int main()
{
    cout << fact(3) << endl; // output=6
    return 0;
}

$ g++ factMain.cpp fact.cpp -o lovecpp -std=c++11

$ lovecpp
6

$ g++ -c factMain.cpp

$ g++ -c fact.cpp

$ g++ factMain.o fact.o -o lovecpp

#include <iostream>
using namespace std;
void swap(int *p, int *q)
{
    int temp;
    temp = *p;
    *p = *q;
    *q = temp;
}
int main()
{
    int a = 3, b = 4;
    cout <<    a << " " << b << endl;
    swap(a , b);
    // 交换之后
    cout <<    a << " " << b << endl;
    /* output:
     3 4
     4 3
     */
    return 0;
}

#include <iostream>
using namespace std;
void swap(int *p, int *q)
{
    int temp;
    temp = *p;
    *p = *q;
    *q = temp;
}
int main()
{
    int a = 3, b = 4;
    cout << a << " " << b << endl;
    swap(&a , &b);
    // 交换之后
    cout << a << " " << b << endl;
    /* output:
4
3
     */
    return 0;
}