AC++第二章答案

2-1 将pad的值改为0即可，其他不做任何变动。

2-2 将pad分解为行空白数与列空白数，因此在对行进行计数和对列进行计数时将分别进行，不会发生冲突。

2-3 源代码：

#include <iostream>#include <string>using std::cin;using std::endl;using std::cout;using std::string;int main() {cout << "Please enter your first name: ";string name;cin >> name;const string greeting = "Hello, " + name + "!";int pad_h = 0; //定义上下边界的间隔int pad_w = 0; //定义左右边界的间隔cout << "Please enter the interval number of the height and the width:"<< endl;cin >> pad_h >> pad_w;const int rows = pad_h * 2 + 3;const string::size_type cols = greeting.size() + pad_w * 2 + 2;cout << endl;for (int r = 0; r != rows; ++r){string::size_type c = 0;while (c != cols) {if (r == pad_h + 1 && c == pad_w + 1) {cout << greeting;c += greeting.size();}else {if (r == 0 || r == rows - 1 || c == 0 || c == cols - 1)cout << "*";elsecout << " ";++c;}}cout << endl;}return 0;}

2-4 源代码：（即定义一个space字符串专门存储空白行的空白字符串，需要注意的是在问候语一行同样需要加上单个空格字符的输入）

#include <iostream>#include <string>using std::cin;using std::endl;using std::cout;using std::string;int main() {cout << "Please enter your first name: ";string name;cin >> name;const string greeting = "Hello, " + name + "!";cout << "Please enter the internal number of the height and the width: ";int pad_h = 0;int pad_w = 0;cin >> pad_h >> pad_w;const int rows = pad_h * 2 + 3;const string::size_type cols = greeting.size() + pad_w * 2 + 2;const string space = string(greeting.size() + pad_w * 2, ' ');cout << endl;for (int r = 0; r != rows; ++r){string::size_type c = 0;while (c != cols) {if (r == pad_h + 1 && c == pad_w + 1) {cout << greeting;c += greeting.size();}else {if (r == 0 || r == rows - 1 ||c == 0 || c == cols - 1){cout << "*";++c;}else if (r == pad_h + 1){cout << " ";++c;}else{cout << space;c += space.size();}}}cout << endl;}return 0;}

2-5 源代码：（此处只要第一个正方形正确写出，后面直接修改即可，均为修改列数）

#include<iostream>#include<string>using namespace std;int main(){int n = 10;//下面首先输出正方形,因为在运行中行距大于字符间距，所以此处将字符间距加宽一倍。//否则直接将space定义为cols－2个,并且还原“* ”为“*”即可。int rows = n;int cols = n;string space = string((cols - 2) * 2, ' ');for (int r = 0; r != rows; r++){string::size_type c = 0;if (r == 0 || r == rows - 1){while (c != cols){cout << "* ";++c;}}else{cout << "* " << space << "*";}cout << endl;}//下面输出长方形，只需要改变每行的space宽度以及首末行的宽度即可rows = n;cols = 2 * n;space = string(cols - 2, ' ');for (int r = 0; r != rows; r++){string::size_type c = 0;if (r == 0 || r == rows - 1){while (c != cols){cout << "*";++c;}}else{cout << "*" << space << "*";}cout << endl;}//下面输出三角形rows = n;cols = 1;for (int r = 0, cols = 1; r != rows; r++, cols++){if (cols < 2)cout << "*" << endl;else {space = string(cols - 2, ' ');string::size_type c = 0;if (r == rows - 1){while (c != cols){cout << "*";++c;}}else{cout << "*" << space << "*";}cout << endl;}}return 0;}

2-6 输出1到10十个整数，不解释。。。

2-7 源代码：

#include<iostream>#include<string>using namespace std;int main(){int i = 10;while (i >= -5) {cout << i << endl;i -= 1;}return 0;}

2-8 源代码：

#include<iostream>#include<string>using namespace std;int main(){int i = 1;int product = 1;while (i < 10){product *= i;++i;}cout << "The product is:" << product;return 0;}

2-9 源代码：（本程序没有考虑到用户可能输入错误的情况，比如用户可能输入字母或者符号等。）

#include<iostream>#include<string>using namespace std;int main(){int a = 1;int b = 1;cout << "Please enter two numbers:" << endl;cin >> a >> b;if (a > b)cout << "Number " << a << " is bigger" << endl;else if (b > a)cout << "Number " << b << " is bigger" << endl;elsecout << "The two numbers is equal." << endl;return 0;}

2-10 第一个std是调用std名称空间中的cout输出流，第二个std同上，由于第一个std只作用在while函数域内，故此处需重新调用。第三个std是调用std名称空间中的endl函数输出换行符。