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练习1-数学计算
让用户输入一个圆的半径，计算这个圆的周长和面积，并输出（保留两位小数）
#include <iostream>
#include <Windows.h>
int main(void) {
float r;
float len;
float s;
std::cout << "请输入半径：";
std::cin >> r;
len = 2 * 3.14 * r;
s = 3.14 * r * r;
std::cout.precision(2);
std::cout.flags(std::cout.fixed);
std::cout << "周长是：" << len << std::endl;
std::cout << "面积是: " << s << std::endl;
system("pause");
return 0;
}
练习2-无符号数的诡异
#include <iostream>
#include <Windows.h>
using namespace std;
int main(void) {
unsigned boyAge;
unsigned girlAge;
unsigned diff;
cout << "美女，多大了?" << endl;
cin >> girlAge; //输入25
cout << "帅哥，多大了?" << endl;
cin >> boyAge; //输入22
diff = girlAge - boyAge;
cout << "美女比帅哥大" << diff <<"岁" << endl;
diff = boyAge - girlAge;
cout << "帅哥比美女大" << diff << "岁" << endl;
system("pause");
return 0;
}
执行结果：
说明：unsigned 类型，就是unsigned int
分析：
在尾部添加如下代码：
unsigned short boyAge2 = boyAge;
unsigned short girlAge2 = girlAge;
unsigned short diff2 = boyAge2 - girlAge2;
cout << "帅哥比美女大" << diff2 << "岁" << endl; //输出65533
结论：
无符号数，不能表示负数！
如果强行用无符号数表示负数，实际存储的是这个负数对应的“补码”
即：该负数 + “模值”
-3 + 65536 = 65533
理解：