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。