(1) for语句 i++

    int count=0;
    for(int i=0; i<6; i++){
        count++;
    }
    cout<<count<<endl;

(2) for语句 i++

    int count=0;
    for(int i=0; i<6; ++i){
        count++;
    }
    cout<<count<<endl;

(3) for语句 i++在循环体中

    int count=0;
    for(int i=0; i<6; ){
        count++;
        i++; // ++i
    }
    cout<<count<<endl;

** 以上三种 count = 6。**

(1) while语句 i--，count=6

    int count=0;
    int i=6;
    while(i--){
        count++;
    }
    cout<<count<<endl;

等同于

    int count=0;
    int i=6;
    while(i){
        i--;
        count++;
    }
    i--; //不可忽略
    cout<<count<<endl;

(2)while语句 --i，count=5

    int count=0;
    int i=6;
    while(--i){
        count++;
    }
    cout<<count<<endl;

等同于

    int count=0;
    int i=6;
    i--;
    while(i){
        count++;
        i--;
    }
    cout<<count<<endl;