c/c++语言开发共享C++自学之路：3.1-简单变量

c++自学之路：3.1-简单变量。

  #include   #include     int main(int argc, const char * argv[]) {            using namespace std;            int n_int = int_max;      short n_short = shrt_max;      long n_long = long_max;      long long n_llong = llong_max;            cout << "int is " << sizeof(n_int) << " bytes." << endl;      cout << "short is " << sizeof(n_short) << " btyes." << endl;      cout << "long is " << sizeof(n_long) << " bytes." << endl;      cout << "long long " << sizeof(n_llong) << " bytes." << endl;      cout << endl;            cout << "maxium values:" << endl;      cout << "int:" << n_int << endl;      cout << "short:" << n_short << endl;      cout << "long:" << n_long << endl;      cout << "long long:" << n_llong << endl;            cout << "minium int values:" << endl;      cout << "bits per byte = " << char_bit << endl;             return 0;  }

sizeof 指出，在使用8位字节的中，int长度为4个字节，可以对类名或者变量名使用sizeof运算符，类名需要放在括号中，变量名括号可选。
cout << "short is " << sizeof(int) << " btyes." << endl;

cout << "short is " << sizeof n_short << " btyes." << endl;

  #include   #define zero 0;  #include     int main(int argc, const char * argv[]) {      using namespace std;            short sam = shrt_max;      unsigned short sue = sam;            cout << "sam has " << sam << " dollars and sue has " << sue;      cout << " dollars deposited." << endl           << "add $1 to each accout." << endl << "now ";            sam = sam + 1;      sue = sue + 1;            cout << "sam has " << sam << " dollars and sue has " << sue;      cout << " dollars deposited.npoor sam!" << endl;            sam = zero;      sue = zero;            cout << "sam has " << sam << " dollars and sue has " << sue;      cout << " dollars deposited." << endl;      cout << "take $1 from each accout." << endl << "now ";            sam = sam - 1;      sue = sue - 1;            cout << "sam has " << sam << " dollars and sue has " << sue;      cout << " dollars deposited." << endl << "lucky sue!" << endl;            return 0;  }    

运行结果：
sam has 32767 dollars and sue has 32767 dollars deposited.
add $1 to each accout.
now sam has -32768 dollars and sue has 32768 dollars deposited.
poor sam!
sam has 0 dollars and sue has 0 dollars deposited.
take $1 from each accout.
now sam has -1 dollars and sue has 65535 dollars deposited.
lucky sue!

short 变量sam 和 unsigned short 变量 sue，分别设置最大值和最小值。short变量从最大值加1，取值从32768变成—32769。unsigned short变量从最大值加1并没有什么问题。short变量从最大值减1，没什么问题。unsigned short变量从最大值加1，从0变为65535。
如果超越了范围，其值将从范围另一端取值。

无符号类型：
unsigned short change;
unsigned int rovert;
unsigned quarterback;//unsigned 本身是 unsigned int 缩写。
unsigned long gone;
unsigned long long lang_lang;
//无符号类型的正值更大。

选择整型类型：
1.int 被设置为对目标计算机而言最为自然的长度。
2.如果变量表示的值不可能为负，如文档中的字数，则可以使用无符号类型，这样可以表示更大的值。

  #include     using namespace std;    int main(int argc, const char * arvg[]) {            using namespace std;      int chest = 42;//10进制      int waist = 0x42;//16进制      int inseam = 042;//8进制            cout << "monsieur cuts a striking figure!n";      cout << "chest = " << chest << " (42 in decimal)n";      cout << "waist = " << waist << " (0x42 in hex)n";      cout << "inseam = " << inseam << " (042 in octal)n" << endl;            //  1.默认情况下cout以十进制显示。            return 0;  }  

  #include     using namespace std;    int main(int argc, const char * arvg[]) {        using namespace std;      int chest = 42;      int waist = 42;      int inseam = 42;            cout << "monsieur cuts a striking figure!" << endl;      cout << "chest = " << chest << " (decimal for 42)" << endl;      cout << hex;      cout << "waist = " << waist << " (hexadecimal for 42)" << endl;      cout << oct;      cout << "inseam = " << inseam << " (octal for 42)" << endl;               //  hex将值转换成16进制显示。oct将值转换成8进制显示。dec将值转换为10进制显示。         return 0;  }  

c++确定常量类型
1.除非有理由将值储存为其他类型，否则c++将整型常量储存为int类型。
2.整数后面l或者l表示long类型，u或者u表示unsigned int 类型，ul表示 unsigned long 类型，ull或者ull表示unsigned long long类型。
3.c++中，对于10进制数值的规则。（int为16位的机器中）20000表示为int类型，40000表示为long类型，3000000000表示为long long 类型。