第6章 函数

Posted 2021-12-13 COCO_PEAK_NOODLE

1-交换2个变量

void swap(int* lhs, int* rhs)
{
    int tmp;
    tmp = *lhs;
    *lhs = *rhs;
    *rhs = tmp;
}

2-&的存在是为了去指针？，然后和拷贝区别开？

void reset(int &i)
{
    i = 0;
}

int main()
{
    int i = 42;
    reset(i);
    std::cout << i  << std::endl;
    return 0;
}

3-使用引用交换数据

void swap(int& lhs, int& rhs)
{
    int temp = lhs;
    lhs = rhs;
    rhs = temp;
}

4-指针是固定值，指针指向的值是固定值

#include <iostream>
using std::cout;

int larger_one(const int i, const int *const p)
{
    return (i > *p) ? i : *p;
}

int main()
{
    int i = 6;
    cout << larger_one(7, &i);

    return 0;
}

5-交换地址，&是变量的别名，指针也是一个变量

//int*& 实际传入的是指针，&意思是别名
void swap(int*& lft, int*& rht)
{
    auto tmp = lft;
    lft = rht;
    rht = tmp;
}

int main()
{
    int i = 42, j = 99;
    auto lft = &i;
    auto rht = &j;

    std::cout << "lft " << lft << std::endl;
    std::cout << "rht " << rht << std::endl;

    swap(lft, rht);
    std::cout << *lft << " " << *rht << std::endl;

    std::cout << "lft " << lft << std::endl;
    std::cout << "rht " << rht << std::endl;

    return 0;
}

输出

lft 0x7ffc3bdddca0
rht 0x7ffc3bdddca4
99 42
lft 0x7ffc3bdddca4
rht 0x7ffc3bdddca0

6-传递数组，感觉现在用vector的多一些吧

#include <iostream>
using std::cout; using std::endl; using std::begin; using std::end;

void print(const int *pi)
{
    if(pi)
        cout << *pi << endl;
}

void print(const char *p)
{
    if (p)
        while (*p) cout << *p++;
    cout << endl;
}

void print(const int *beg, const int *end)
{
    while (beg != end)
        cout << *beg++ << endl;
}

void print(const int ia[], size_t size)
{
    for (size_t i = 0; i != size; ++i) {
        cout << ia[i] << endl;
    }
}

void print(int (&arr)[2])
{
    for (auto i : arr)
        cout << i << endl;
}

int main()
{
    int i = 0, j[2] = { 0, 1 };
    char ch[5] = "pezy";
    
    print(ch);
    print(begin(j), end(j));
    print(&i);
    print(j, end(j)-begin(j));
    print(j);
    
    return 0;
}

7- int强转string

在这里插入代码片

8-如何定义函数指针类型，及使用

#include <iostream>
#include <string>
#include <vector>
using std::vector; using std::cout;

//
// @brief Exercise 6.54
// @note  define the function type fp
//
inline int f(const int, const int);
typedef decltype(f) fp;//fp is just a function type not a function pointer

//
// @brief Exercise 6.55
// @note  Store pointers to these functions in the vector
//
inline int NumAdd(const int n1, const int n2)  { return n1 + n2; }
inline int NumSub(const int n1, const int n2)  { return n1 - n2; }
inline int NumMul(const int n1, const int n2)  { return n1 * n2; }
inline int NumDiv(const int n1, const int n2)  { return n1 / n2; }

vector<fp*> v{ NumAdd, NumSub, NumMul, NumDiv };

int main()
{
    //
    // @brief Exercise 6.56
    // @note  Call each element in the vector and print their result.
    //
    for (auto it = v.cbegin(); it != v.cend(); ++it)
        cout << (*it)(2, 2) << std::endl;

    return 0;
}

9-最简单的递归

int fact(int val)
{
    if (val == 0 || val == 1) return 1;
    else return val * fact(val-1);
}