分别用+while+循环，+do+while+循环以及+for+实现一到二十的阶乘

1.使用while循环实现一到二十的阶乘的代码如下：

int i = 1;
int result = 1;
while(i <= 20){
    int j = 1;
    int factorial = 1;
    while(j <= i){
        factorial *= j;
        j++;
    }
    result += factorial;
    i++;
}
System.out.println(result);

2.使用do-while循环实现一到二十的阶乘的代码如下：

int i = 1;
int result = 1;
do{
    int j = 1;
    int factorial = 1;
    do{
        factorial *= j;
        j++;
    }while(j <= i);
    result += factorial;
    i++;
}while(i <= 20);
System.out.println(result);

3.使用for循环实现一到二十的阶乘的代码如下：

int result = 1;
for(int i = 1; i <= 20; i++){
    int factorial = 1;
    for(int j = 1; j <= i; j++){
        factorial *= j;
    }
    result += factorial;
}
System.out.println(result);