Question

用java程序写出一个程序求1!+2!+3!+...20!的值

Answer 1

你看看能用么:
public class A {
public static void main(String[] args) {
int i = test(20);
System.out.println(i);
}

private static int test(int i) {
int sum = 0;
for (int j = 1; j <= i; j++) {
sum += fn(j);
}
return sum;
}

private static int fn(int j) {
int value = 0;
if (j == 0 || j == 1) {
return j;
} else {
value = j * fn(j - 1);
}
return value;
}

}

Answer 2

public class test {

public static void main(String[] args) {
int f=1;
long result=0;
for(int i=1;i<21;i++){
f=f*i;
result+=f;
}
System.out.println(result);
}

}

Answer 3

public class Tt {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int k=0;
for(int i=1;i<21;i++){
k=k+i;
System.out.print(i+"+");
}
System.out.print("="+k);
}
}

Answer 4

public class ff {
//乘阶算法
public static int fun(int num){
if(num==0||num==1){
return 1;
}else{
return num*fun(num-1);
}
}
public static void main(String[] args) {
//算20的阶乘
System.out.println("结果："+ff.fun(20));
}

}