C++ Primer Answer ch05

5.1

空语句是;

在程序的某个地方，语法上需要一条语句但是逻辑上不需要，此时应该使用空语句。

5.2

块（复合语句）是指用花括号括起来的（可能为空的）语句和声明的序列

如果在程序的某个地方，语法上需要一条语句，但是逻辑上需要多条语句，则应该使用复合语句

5.3

#include <iostream>

using namespace std;

int main()
{
    int sum = 0, val = 1;
    while(val <= 10)
    {
        sum += val;
        ++val;
    }
    cout << "Sum of 1 to 10 inclusive is " << sum << endl;

    sum = 0;
    val = 0;
    while(++val, val <= 10)
        sum += val;
    cout << "Sum of 1 to 10 inclusive is " << sum << endl;
    return 0;
}

5.4

#include <iostream>

using namespace std;

bool find(int)
{
    return true;
}

int main()
{
    /*
    string s = "132";
    string::iterator iter = s.begin();
    while(iter != s.end())
        ;
    */
    int word = 2;
    while(bool status = find(word))
    {

    }
    //status was not declared//if(!status)
    //;
    return 0;
}

5.5

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<string> s = {"A", "B", "C"};
    int grade;
    while(cin >> grade)
    {
        if(grade >= 100)
            cout << s[0] << endl;
        else
            if(grade >= 60)
                cout << s[1] << endl;
            else
                cout << s[2] << endl;
    }
    return 0;
}

5.6

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<string> s = {"A", "B", "C"};
    int grade;
    while(cin >> grade)
    {
        (grade >= 100) ? (cout << s[0] << endl) :
                                (grade >= 60) ? (cout << s[1] << endl) : (cout << s[2] << endl);
    }
    return 0;
}

5.7

#include <iostream>

using namespace std;

int main()
{
    //a
    if(ival1 != ival2)
        ival1 = ival2;
    else
        ival1= ival2 = 0;
    //b
    if(ival < minval)
    {
        minval = ival;
        occurs = 1;
    }
    //c
    int ival;
    if(ival = get_value())
        cout << "ival = " << ival << endl;
    if(!ival)
        cout << "ival = 0\n";
    //d
    if(ival == 0)
        ival = get_value();
    return 0;
}

5.8

悬垂else：else和if的匹配问题

C++规定else与离它最近的尚未匹配的if匹配

5.9

#include <iostream>

using namespace std;

int main()
{
    char ch;
    int vowelCnt = 0;
    while(cin >> ch)
    {
        switch(ch)
        {
            case 'a':
            case 'e':
            case 'i':
            case 'o':
            case 'u':
                ++vowelCnt;
                break;
            default:
                ;
        }
    }
    cout << vowelCnt;
    return 0;
}

5.10

#include <iostream>

using namespace std;

int main()
{
    char ch;
    int vowelCnt = 0;
    while(cin >> ch)
    {
        switch(ch)
        {
            case 'a':
            case 'A':
            case 'e':
            case 'E':
            case 'i':
            case 'I':
            case 'o':
            case 'O':
            case 'u':
            case 'U':
                ++vowelCnt;
                break;
            default:
                ;
        }
    }
    cout << vowelCnt;
    return 0;
}

5.11

#include <iostream>

using namespace std;

int main()
{
    char ch;
    int spaceCnt = 0, tCnt = 0, nCnt = 0;
    int otherCnt = 0;
    //cin >> ch遇到空格等结束
    while(cin.get(ch))
    {
        switch(ch)
        {
            case ' ':
                ++spaceCnt;
                break;
            case '\t':
                ++tCnt;
                break;
            case '\n':
                ++nCnt;
                break;
            default:
                ++otherCnt;
                ;
        }
    }
    cout << spaceCnt << endl
         << tCnt << endl
         << nCnt << endl
         << otherCnt << endl;
    return 0;
}

5.12

#include <iostream>

using namespace std;

int main()
{
    char ch;
    char prech = '\0';
    int ffCnt = 0, flCnt = 0, fiCnt = 0;

    while(cin.get(ch))
    {
        if(prech == 'f')
        {
            switch(ch)
            {
                case 'f':
                    ++ffCnt;
                    break;
                case 'l':
                    ++flCnt;
                    break;
                case 'i':
                    ++fiCnt;
                    break;
                default:
                    ;
            }
        }
        prech = ch;
    }
    cout << ffCnt << endl
         << flCnt << endl
         << fiCnt << endl;
    return 0;
}

5.13

//a
/*
unsigned cCnt = 0, eCnt = 0, iouCnt = 0;
char ch = next_text();
switch(ch)
{
case 'a':
    ++aCnt；
    break;
case 'b':
    eCnt++;
    break;
default:
    ++iouCnt;
}
*/

//b
/*
unsigned index = some_value();
int ix;
switch(index)
{
case 1:
    ix = get_value();
    ivec[ix] = index;
    break;
default:
    ix = ivec.size() - 1;
    ivec[ix] = index;
}
*/

//c
unsigned evenCnt = 0, oddCnt = 0;
int digit = get_num() % 10;
switch(digit)
{
case 1:
case 3:
case 5:
case 7:
case 9:
    ++oddCnt;
    break;
case 0:
case 2:
case 4:
case 6:
case 8:
    ++evenCnt;
    break;
}

//d
const unsigned ival = 512, jval = 1024, kval = 4096;
unsigned bufsize;
unsigned swt = get_bufCnt();
switch(swt)
{
case ival:
    bufsize = ival * sizeof(int);
    break;
case jval:
    bufsize = jval * sizeof(int);
    break;
case kval:
    bufsize = kval * sizeof(int);
    break;
}

5.14

#include <iostream>
#include <vector>

using namespace std;

int main()
{
    string word;
    int cnt = 1;
    int cntMax = 1;
    string compareword;
    string wordMax;
    while(cin >> word)
    {
        if(word == compareword)
            ++cnt;
        else
            cnt = 1;
        if(cnt > cntMax)
        {
            wordMax = compareword;
            cntMax = cnt;
        }
        compareword = word;
    }
    if(cntMax > 1)
        cout << cntMax << ' ' << wordMax;
    else
        cout << "There is no repeated word.";
    return 0;
}

5.15

//a
int ix;
for(ix = 0; ix != sz; ++ix)
{

}
if(ix != sz)
    ;

//b
int ix;
for(; ix != sz; ++ix)
    ;

//c
for(int ix = 0; ix != sz; ++ix)
    ;

5.16

#include <iostream>

using namespace std;

int main()
{
    const size_t a_size = 3;
    int a[a_size] = {1, 2, 3};
    size_t i = 0;
    for(; i != a_size; ++i)
        cout << a[i] << endl;
    cout << endl;
    i = 0;
    while(i != a_size)
    {
        cout << a[i] << endl;
        ++i;
    }
    return 0;
}

for更灵活

5.17

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> a{0, 1, 1, 2};
    vector<int> b{0, 1, 1, 2, 3, 5, 8};
    vector<int>::size_type len;
    (a.size() <= b.size()) ? (len = a.size()) : (len = b.size());
    for(decltype(a.size()) i = 0; i != len; ++i)
    {
        if(a[i] != b[i])
        {
            return 1;
        }
    }
    cout << "Y";
    return 0;
}

5.18

#include <iostream>

using namespace std;

int get_response(void)
{
    return 1;
}
int main()
{
    //a
    /*
    do{
        int v1. v2;
        cout << "Please enter two numbers to sum:";
        if(cin >> v1 >> v2)
            cout << "Sum is:" << v1 + v2 << endl;
    }while(cin)
    */

    //b
    /*
    int ival;
    do{

    }while(ival = get_response());
    */
    //c
    int ival = get_response();
    do{

    }while(ival);

    return 0;
}

5.19

#include <iostream>

using namespace std;

int main()
{
    string s1, s2;
    do
    {
        cin >> s1 >> s2;
        if(s1.size() <= s2.size())
            cout << s1 << endl;
        else
            cout << s2 << endl;
    }while(cin);
    return 0;
}

5.20

#include <iostream>

using namespace std;

int main()
{
    string word;
    string compareWord;
    int flag = 0;
    while(cin >> word)
    {
        if(word == compareWord)
        {
            cout << word << endl;
            flag = 1;
            break;
        }
        compareWord = word;
    }
    if(flag == 0)
        cout << "no matching";
    return 0;
}

5.21

#include <iostream>
#include <cctype>

using namespace std;

int main()
{
    string word;
    string compareWord;
    int flag = 0;
    while(cin >> word)
    {
        if(!isupper(word[0]))
            continue;
        if(word == compareWord)
        {
            cout << word << endl;
            flag = 1;
            break;
        }
        compareWord = word;
    }
    if(flag == 0)
        cout << "no matching";
    return 0;
}

5.22

/*
begin:
    int sz = get_size();
    if(sz <= 0)
    {
        goto begin;
    }
*/
do{
    int sz = get_size();
}while(sz <= 0);

5.23

#include <iostream>
#include <stdexcept>

using namespace std;

int main()
{
    int a, b;
    while(cin >> a >> b)
    {
        try{
            if(b == 0)
                throw runtime_error("b must != 0");
            cout << a / b << endl;
        }catch(runtime_error e){
            cout << e.what();
            return 1;
        }
    }
    return 0;
}

5.24

#include <iostream>
#include <stdexcept>

using namespace std;

int main()
{
    int a, b;
    while(cin >> a >> b)
    {
        if(b == 0)
            throw runtime_error("b must != 0");
        cout << a / b << endl;
    }
    return 0;
}

5.25

#include <iostream>
#include <stdexcept>

using namespace std;

int main()
{
    int a, b;
    while(cin >> a >> b)
    {
        try{
            if(b == 0)
                throw runtime_error("b must != 0");
            cout << a / b << endl;
        }catch(runtime_error e){
            cout << e.what();
            cout << "\nTry again?(y/n)";
            char ch;
            cin >> ch;
            if(!cin || ch == 'n')
                break;
            else
            {
                cin >> b;
                if(b == 0)
                    break;
                cout << a / b << endl;
            }
        }
    }
    return 0;
}