《C++ Primer Plus（第六版）》（7）（第五章 循环和关系表达式 答案）

5.8 复习题

1.入口条件就是在进入循环的时候就检测，出口条件是先进入循环，再检测，至少可以执行一次循环。

for、while属于入口条件检测，do while属于出口条件检测。

2.
01234

int i;
for (i = 0; i < 5; i++)
cout << i;
cout << endl;

3.
0369
12

int j;
for (j = 0; j < 11; j += 3)
cout << j;
cout << endl << j << endl;

4.
6
8

int j = 5;
while (++j < 9)
{
    cout << j++ << endl;
}

5.

k = 8

int k = 8;
do
	cout << "k = " << k << endl;
while (k++ < 5);

6.

for (int i = 1; i <= 64; i *= 2)
{
	cout << i<<" ";
}
cout << endl;

7.使用{}，其实就算只有一条语句，也应该使用{}，可以是代码更加清晰，而且说不定什么时候需求就要变了，一条语句通常干不了什么的。

8.都有效。

int x = (1, 024);//x为20，（）内返回024，0开头是8进制，即是20.
int y;
y = 1, 024;//y=1，之后024.就没了

9.cin>>ch,跳过空格、换行符、制表符。cin.get(ch) 和 ch = cin.get()可以读取这些字符

5.9编程题

1.

int m = 0;
int n = 0;
cin >> m;
cin >> n;
if (m > n) {
    int t = m;
    m = n;
    n = t;
}
int total = 0;
for (int i = m; i <= n; i++) {
    total += i;
}
cout << total <<endl;

2.

5.4程序清单

const int ArSize = 16;
long long factorials[ArSize];
factorials[1] = factorials[0] = 1LL;
for (int i = 2; i < ArSize; i++) {
    factorials[i] = i * factorials[i-1];
}
for (int i = 0; i < ArSize; i++) {
    cout << i << " = " << factorials[i] << endl;
}

修改后：

    const int ArSize = 101;
    array<long double, ArSize> factorials;
    factorials[1] = factorials[0] = 1;
    for (int i = 2; i < ArSize; i++) {
        factorials[i] = i * factorials[i-1];
    }
    for (int i = 0; i < ArSize; i++) {
        cout << i << " = " << factorials[i] << endl;
    }

结果：

0 = 1

1 = 1

2 = 2

3 = 6

4 = 24

5 = 120

6 = 720

7 = 5040

8 = 40320

9 = 362880

10 = 3.6288e+06

11 = 3.99168e+07

12 = 4.79002e+08

13 = 6.22702e+09

14 = 8.71783e+10

15 = 1.30767e+12

。。。好长

3.

cout << "Please enter:" << endl;
int i = -1;
int total = 0;
while (i != 0) {
    cin >> i;
    total += i;
    cout << "current sum: "<< total << endl;
}

4.

const double base = 100;
const double interestA = 0.1;
const double interestB = 0.05;
double moneyA = base;
double moneyB = base;
int year = 0;
while (moneyA >= moneyB) {
    ++year;
    moneyA += (base * interestA);
    moneyB += (moneyB * interestB);
}
cout << "Year:" << year << " A:" << moneyA << " B:" << moneyB << endl;

结果：

Year:27 A:370 B:373.346

5.

string month[12] = {
    "January","February","March","April",
    "May","June","July","August",
    "September","October","November","December"};
int total = 0;
int thisYearData[12];
for (int i = 0; i < 12; ++i) {
    cout << "Please enter " << month[i] <<"'data:" ;
    cin >> thisYearData[i];
    total += thisYearData[i];
}
cout << "this year' data: "<< total <<endl;

6.

string month[12] = {
    "January","February","March","April",
    "May","June","July","August",
    "September","October","November","December"};
int total = 0;
int yearData[3][12];
int yearTotal[3];
for (int j = 0; j < 3; ++j) {
    for (int i = 0; i < 12; ++i) {
        cout << "Please enter the " << j + 1 << " year " << month[i] <<"'data:" ;
        cin >> yearData[j][i];
        total += yearData[j][i];
        yearTotal[j] += yearData[j][i];
    }
}
for (int i = 0; i < 3; ++i) {
    cout << "year:"<< i + 1 << " data:"<< yearTotal[i] << endl;
}
cout << "all year' data: "<< total <<endl;

7.

struct SCar
{
    string manufacturer;
    int year;
};
int num = 0;
cout << "How many cars do you wish to catalog?";
cin >> num;
cin.get();
SCar* carArr =  new SCar[num];
for (int i = 0; i < num; ++i ) {
    cout<< "Car #" << i + 1 << ":"<<endl;
    cout<< "Please enter the make:";
    getline(cin, carArr[i].manufacturer);
    cout << "Please enter the year made:";
    cin >> carArr[i].year;
    cin.get();
}
cout << "Here is your collection:" << endl;
for (int i = 0 ; i < num; ++i) {
    cout << carArr[i].year << " " << carArr[i].manufacturer << endl;
}

8.

char s[20];
int count = 0;
cout << "Enter words (to stop, type the word done):" <<endl;
while (true) {
    cin >> s;
    if (0 == strcmp(s, "done")) {
        break;
    }else{
        ++count;
    }
}
cout << "You entered a total of " << count << " words" << endl;

9.

string s;
int count = 0;
cout << "Enter words (to stop, type the word done):" <<endl;
while (true) {
    cin >> s;
    if (s == "done") {
        break;
    }else{
        ++count;
    }
}
cout << "You entered a total of " << count << " words" << endl;

10.

cout << "Enter number of rows: ";
int n = 0;
cin >> n;
for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n ; ++j) {
        if (j < n - i - 1) {
            cout << "." ;
        }else{
            cout << "*";
        }
    }
    cout << endl;
}