重新实践c++primer上面的代码

又重新敲了敲c++primer上面的代码，觉得很有意思，讲的很细，c++真牛逼啊

#include <iostream>
#include <string>
#include <cctype>
#include <vector>
#include <cassert>
using namespace std;
using std::ostringstream;

int Add()
{
    cout << "enter two numbers" << endl;

    int v1 = 0, v2 = 0;
    cin >> v1 >> v2;
    cout << "the sum of" << v1 << "and" << v2
        << "is" << v1 + v2 << endl;
    return 0;
}

int Unsigned()
{
    unsigned u = 10, u2 = 42;
    cout << u2 - u << endl;
    cout << u - u2 << endl;

    int i = 10, i1 = 42;
    cout << i - i1 << endl;
    cout << i1 - i << endl;

    u = 42;
    i = 10;
    cout << i - u << endl;
    cout << u - i << endl;

    u = 10;
    i = -42;
    cout << i + i << endl;
    cout << u + i << endl;

//     u = 10;
//     cout << "hehe" << endl;
//     while (u >= 0)
//     {
//         cout << u << endl;
//         u--;
//     }
    return 0;
}

int reused = 42;

int Scope_Levels()
{
    int unique = 0;
    
    cout << reused << "" << unique << endl;
    int reused = 0;
    cout << reused << "" << unique << endl;
    cout << ::reused << "" << unique << endl;
    return 0;
}

int ReferenceTest()
{
    int i = 0, &ri = i;

    cout << i << " " << ri << endl;
    i = 4;
    cout << i << " " << ri << endl;

    ri = 10;
    cout << i << "  " << ri << endl;
    
    return 0;
}

int CompoundRef()
{
    int i = 1024, *p = &i, &r = i;
    cout << i << " " << *p << " " << r << endl;

    int j = 42, *p2 = &j;
    int *&pref = p2;
    cout << *pref << endl;

    pref = &i;
    cout << *pref << endl;

    *pref = 0;
    cout << i << " " << *pref << " " << *p2 << endl;

    return 0;
}

// int Convs()
// {
//     int i = 42;
//     cout << i << endl;
// 
//     if (i)
//         i = 0;
//     cout << i << endl;
// 
//     bool b = 42;
//     cout << b << endl;
// 
//     int j = b;
//     cout << j << endl;
// 
//     double pi = 3.14;
//     cout << pi << endl;
// 
//     j = pi;
//     cout << j << endl;
// 
//     unsigned char c = -1;
//     i = c;
//     cout << i << endl;
//     
//     return 0;
// }

int TestDoublePtr()
{
    int ival = 1024;
    int* pi = &ival;
    int** ppi = &pi;

    cout << ival << "   " << *pi << "    " << **ppi << endl;

    int i = 2;
    int* p1 = &i;

    *p1 = *p1 * *p1;
    cout << "i = " << i << endl;

    *p1 *= *p1;
    cout << "i = " << i << endl;
    return 0;
}

int TestDecltype()
{
    int a = 0;
    decltype(a) c = a;
    decltype((a)) d = a;

    c++;
    cout << "a" << a << "c" << c << "d" << d << endl;

    d++;
    cout << "a" << a << "c" << c << "d" << d << endl;

    int A = 0, B = 0;
    decltype((A)) C = A;
    decltype(A = B) D = A;

    C++;
    cout << A << C << D << endl;
    D++;
    cout << A << C << D << endl;

    return 0;
}

int TestCctype()
{
    string s("Hello World!!!");
    //     for (auto c : s)
    //         cout << c << endl;

    string::size_type punct_cnt = 0;
    for (string::size_type c = 0; c != s.size(); c++)
        if (ispunct(s[c]))
            ++punct_cnt;
    cout << punct_cnt << "        " << s << endl;

    string orig = s;
    for (string::size_type c = 0; c != s.size(); c++)
        s[c] = toupper(s[c]);
    cout << s << endl;

    s = orig;
    string::size_type index = 0;
    while (index != s.size() && !isspace(s[index]))
    {
        s[index] = toupper(s[index]);
        index++;
    }
    cout << s << endl;

    return 0;
}

int TestArrayScores()
{
    vector<unsigned> grades;
    const size_t sz = 11;
    unsigned scores[sz] = {};
    unsigned grade;

    while(cin >> grade)
    {
        if (grade <= 100)
            scores[grade / 10]++;
        grades.push_back(grade);
    }
    cout << "grades.size = " << grades.size() << endl;

    for (vector<unsigned>::const_iterator g = grades.begin(); g != grades.end(); g++)
        cout << *g << " ";
    cout << endl;

    for (size_t i = 0; i != sz; i++)
        cout << scores[i] << " ";
    cout << endl;
    return 0;

}

int TestGetline()
{
    string line;
    while (getline(cin, line))
        cout << line << endl;
    return 0;
}

int TestCstring()
{
    string s1 = "A string example";
    string s2 = "A different string";

    if (s1 < s2)
        cout << s1 << endl;
    else
        cout << s2 << endl;

    const char ca1[] = "A string example";
    const char ca2[] = "A string example";

    if (strcmp(ca1, ca2) < 0)
        cout << ca1 << endl;
    else
        cout << ca2 << endl;

    const char *cp1 = ca1, *cp2 = ca2;
    cout << strcmp(cp1, cp2) << endl;
    cout << strcmp(cp2, cp1) << endl;
    cout << strcmp(cp1, cp1) << endl;

    cout << strlen(cp1) << endl;

    const unsigned sz = 16 + 18 + 2;
    //char largeStr[sz];
    //pass
    return 0;
}

int TestIterator()
{
    string str("some string"), orig = str;
    if (!str.empty())
        cout << str[0] << endl;
    if (!str.empty())
        str[0] = toupper(str[0]);
    cout << str << endl;

    str = orig;

    if (str.begin() != str.end()) 
    {
        string::iterator it = str.begin();
        *it = toupper(*it);
    }
    cout << str << endl;

    str = orig;
    for (string::size_type index = 0; index != str.size() && !isspace(str[index]); index++)
        str[index] = toupper(str[index]);
    cout << str << endl;

    str = orig;
    for (string::iterator it = str.begin(); it != str.end() && !isspace(*it); it++)
        *it = toupper(*it);
    cout << str << endl;

    str = orig;
    string::size_type index = 0;
    while (index != str.size() && !isspace(str[index]))
    {
        str[index] = toupper(str[index]);
        index++;
    }
    cout << str << endl;

    string::iterator beg = str.begin();
    while (beg != str.end() && !isspace(*beg))
    {
        *beg = toupper(*beg);
        beg++;
    }
    cout << str << endl;

    str = orig;
    for (string::const_iterator c = str.begin(); c != str.end(); c++)
        cout << *c;
    cout << endl;
    for (string::iterator c = str.begin(); c != str.end(); c++)
        *c = '*';
    cout << str << endl;

    str = orig;
    for (string::size_type ix = 0; ix != str.size(); ix++)
        cout << str[ix];
    for (string::size_type ix = 0; ix != str.size(); ++ix)
        str[ix] = '*'; 
    cout << str << endl;

    return 0;

}

int arr[10];
int *p1[10];
int(*p2)[10] = &arr;

typedef int arrT[10];

arrT* func(int i);
int(*func(int i))[10];

int odd[] = { 1, 3, 5, 7, 9 };
int even[] = { 0, 2, 4, 6, 8 };

int* elemPtr(int i)
{
    return (i % 2) ? odd : even;
}

int(*arrPtr(int i))[5]    
{
    return (i % 2) ? &odd : &even;
}

int (&arrRef(int i))[5]
{
    return (i % 2) ? odd : even;
}

int TestBefore1()
{
    int* p = elemPtr(6);
    int(*arrP)[5] = arrPtr(5);
    int(&arrR)[5] = arrRef(4);

    for (size_t i = 0; i < 5; i++)
        cout << p[i];
    cout << endl;
    for (size_t i = 0; i < 5; i++)
        cout << (*arrP)[i];
    cout << endl;
    for (size_t i = 0; i < 5; i++)
        cout << arrR[i];
    return 0;
}

// struct ErrCode 
// {
//     ErrCode(int i) : num(i) {}
//     string msg()
//     {
//         ostringstream s;
//         s << "ErrCode" << num;
//         return s.str();
//     }
//     int num;
// };

string::size_type sumLength(const string&, const string&);
string::size_type latgerLength(const string&, const string&);

string::size_type sumLength(const string& s1, const string& s2)
{
    return s1.size() + s2.size();
}

string::size_type largerLength(const string& s1, const string& s2)
{
    return (s1.size() > s2.size()) ? s1.size() : s2.size();
}

string::size_type(*getFcn(const string& fetch))(const string&, const string&)
{
    if (fetch == "sum")
        return sumLength;
    return largerLength;
}

int TestBefore2()
{
    cout << getFcn("sum")("hello", "world") << endl;
    cout << getFcn("larger")("hello", "world") << endl;
    return 0;
}

inline const string&
shorterString(const string& s1, const string& s2)
{
    return s1.size() <= s2.size() ? s1 : s2;
}

int TestBefore3()
{
    string s1("successes"), s2("failure");
    cout << shorterString(s1, s2) << endl;
    cout << shorterString(s1, s2).size() << endl;
    cout << (s1.size() < s2.size() ? s1 : s2) << endl;
    return 0;
}

void print(const int ia[], size_t size)
{
#ifndef NDEBUG
    cerr << "print(int *, size_t)" << "  " << size << endl;
#endif
}

int TestErrorDeal()
{
    string word = "foo";
    const string::size_type threshold = 5;
    if (word.size() < threshold)
        cerr << "Error: " << __FILE__
        << " : in function " << TestErrorDeal
        << " at line " << __LINE__ << endl
        << "       Compiled on " << __DATE__
        << " at " << __TIME__ << endl
        << "       Word read was \"" << word
        << "\":  Length too short" << endl;
    word = "something longer than five chars";
    assert(word.size() > threshold);

    return 0;
}

这些东西一定是敲过一遍才觉得有趣，当然上边的东西也很初级，这基本上是前四章内重要的函数了，把它们弄在了一起，暂时先不整理了