《C++PrimerPlus（第六版）》（7）（第五章循环和关系表达式答案）

《C++PrimerPlus（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;
}。