JAVA阶乘

public class jiecheng {

public static void main(String args[]) {
long a, u, b;
u = 1;
b = 0;
String str = null;
for (a = 1; a <= 20; a++) {
u = u * a;
b = b + u;
if (a == 1) {
str = a + "!";
} else {
str = str + "+" + a + "!";
}
System.out.println(str + "=" + b);
}

}
}

写出注释就行

public class jiecheng {

public static void main(String args[]) {
long a, u, b;//定义三个变量,分别名为a,u,b
u = 1;//u初始1
b = 0;//b初始0
String str = null;//定义一个名为str的字符串变量初始为空
for (a = 1; a <= 20; a++) {//让a变量从1变到20
u = u * a;//算出当前a所存值的价乘
b = b + u;//把这个数加到变量b中去
if (a == 1) {
str = a + "!";//判断当前a的值,是1的话前str的值为1!
} else {
str = str + "+" + a + "!";//如果不是1则把str内的值为上当前a的值再加上!(阶乘符号)赋给str变量
}
System.out.println(str + "=" + b);//输出当前str的值
}

}
}//所以最后输出结果为

//

1!=1
1!+2!=3
1!+2!+3!=9
1!+2!+3!+4!=33
1!+2!+3!+4!+5!=153
1!+2!+3!+4!+5!+6!=873
1!+2!+3!+4!+5!+6!+7!=5913
1!+2!+3!+4!+5!+6!+7!+8!=46233
1!+2!+3!+4!+5!+6!+7!+8!+9!=409113
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!=4037913
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!=43954713
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!=522956313
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!=6749977113
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!+14!=93928268313
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!+14!+15!=1401602636313
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!+14!+15!+16!=22324392524313
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!+14!+15!+16!+17!=378011820620313
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!+14!+15!+16!+17!+18!=6780385526348313
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!+14!+15!+16!+17!+18!+19!=128425485935180313
1!+2!+3!+4!+5!+6!+7!+8!+9!+10!+11!+12!+13!+14!+15!+16!+17!+18!+19!+20!=2561327494111820313

public class jiecheng {

public static void main(String args[]) { long a, u, b; //定义变量 u = 1; b = 0; // u=1 b=0 String str = null; for (a = 1; a <= 20; a++) { u = u * a; //循环算出阶乘的值 b = b + u; if (a == 1) { str = a + "!"; //如果是1就打出 1! } else { str = str + "+" + a + "!"; //分别输出 1！+2！+。。。。 } System.out.println(str + "=" + b); //结果打出 1!+2!+...+20!=所算出的b的值。 }

} }

晕

用递归啊

int chengjie(int i){

if(i==1) return 1;

else if(i>1){ return chengjie(i-1)*i;

else {System.out.println("this cna't number a ");]

}

}

public static void main(String[] args) { // TODO Auto-generated method stub long a, u, b;//定义了三个long类型的变量 u = 1;//初始化u=1 b = 0;//初始化b=0 String str = null;//定一个string类型的str为null for (a = 1; a <= 20; a++) {//a=1 a小于等于20 那么就是循环20次 a的值是从1-20 u = u * a;//当a=1时 u = 1*1 当a=2时 u=1*2 当a=3时 u=2*3依次类推到a=20 b = b + u;// 其实就是累加u 这样的算法不是阶乘吧 上面的那个u最终已经是阶乘的结果了 if (a == 1) {//当a==1的时候 str = a + "!";//字符串str = 这个 条件是a==1 } else {// str = str + "+" + a + "!";//否则str=原来的str+这个 字符串连接也就是在a=2--10的时候输出 } } System.out.println(str + "=" + b);//最后输出 }