在Java中使用Scanner类打印X1-X3 + X5…n

Question

I was trying to print the following series: X ¹ -X ³ +X ⁵ -X ⁷ .......X ⁿ

I have done everything but struck on changing the sign.
Anybody has idea?

Here is the code:

int n=10;int sum=0;int x=2;

double d=0.00;
for(int i=1;i<=n;i++){
    d = Math.pow(x,i);
    sum = sum + (int)d;
}

Answer 1

you should do some steps:

First way

• use a boolean and name it as SIGN

  • change it's value each time you reach end of loop to determine sign based on 1 or 0 (true or false)
    • if sign was true use +
    • if sign was false use -

• increase i in for loop twice ( i+=2 ) each time, so values of i will be 1, 3, 5, ...

---

int n=10;int sum=0;int x=2;

double d=0.00;
boolean sign = true;
for(int i=1; i<=n ; i+=2 ){
    d=Math.pow(x,i);
    sum += ((sign)?(int)d:(-1*(int)d));
    sign = !sign;
}

Second way

• use an integer and name it as SIGN
  • change it's value each time you reach end of loop to determine sign based on 1 or -1.
• since it has the same type as the iterator variable, you can define it in the loop.

---

int n=10;int sum=0;int x=2;

for (int i = 1, sign = 1; i <= n; i += 2, sign = -sign) {
    sum += sign * (int)Math.pow(x, i);
}

Answer 2

you can input parameters by Scanner and change the sign by Math.pow(-1,n) . code is as follows.

int sum = 0;
Scanner input = new Scanner(System.in);
System.out.println("please enter n:");
int n = input.nextInt();
System.out.println("please enter x:");
int x = input.nextInt();
for(int i = 1; i <= n; i += 2){
    sum += (int)Math.pow(-1, (i-1)/2) * Math.pow(x, i);
}