自加++

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i++使用後加1

++i使用前加1

 

那麼 int a=++i  +  ++i;

是怎麼樣計算的呢？

++i;

++i;

a=i+i=2+2=4;

 

而i++是如何計算的呢

a=i++ + i++;

先執行a=i+i;

然後i++;

i++;

讓我們看下面的代碼

// 例1#include <iostream>#include <cstdlib>using namespace std;void main(){    int c = 0, a = 0, b = 0;    cout<<"兩次次使用 ++a"<<endl;    c =  (++a) + (++a);     cout<<"the value of c is "<<c<<endl;    c = a + a;    cout<<"the value of c is "<<c<<endl<<endl;        cout<<"兩次次使用 b++"<<endl;    c = (b++) + (b++);    cout<<"the value of c is "<<c<<endl;    c = b + b;    cout<<"the value of c is "<<c<<endl<<endl;    a = 0;//先重新初始化下 變數a    cout<<"a++ 與 ++a 的混合使用, a++在前"<<endl;    c =  (++a) + (a++);     cout<<"the value of c is "<<c<<endl;    c = a + a;    cout<<"the value of c is "<<c<<endl<<endl;    a = 0;//先重新初始化下 變數a    cout<<"a++ 與 ++a 的混合使用, a++在後"<<endl;    c = (a++) + (++a);     cout<<"the value of c is "<<c<<endl;    c = a + a;    cout<<"the value of c is "<<c<<endl<<endl;    a = 0;//先重新初始化下 變數a    cout<<"一個 a++ 與 兩個 ++a 的混合使用"<<endl;    c = (a++) +(++a) + (++a);     cout<<"the value of c is "<<c<<endl;    c = a + a + a;    cout<<"the value of c is "<<c<<endl<<endl;    a = 0;//先重新初始化下 變數a    cout<<"兩個 a++ 與 一個 ++a 的混合使用"<<endl;    c = (a++) + (a++) + (++a);     cout<<"the value of c is "<<c<<endl;    c = a + a + a;    cout<<"the value of c is "<<c<<endl<<endl;    system("pause");}

執行結果如：