要从系列中打印答案-> x ^ 3-x ^ 5 + x ^ 7-x ^ 9 +

Question

#include<stdio.h>
#include<conio.h>
#include<math.h>
int main()
    {
        int x,n;
        float sum=0;
        printf("Length and Value");
        scanf("%d%d",&n,&x);

        for(int i=1;i<=n;i++)
        {
            sum+=(pow(x,2*i+1) * pow(-1,i+1));
        }
        printf("%f",sum);
        return 0;
    }

I'm trying to solve this series in C language. Am I doing something wrong in the above code?

Answer 1

Yes, you're a bit wrong. In your code

 printf("%f",sum);

sum is an int and using %f to print the value of an int is undefined behaviour .

The function pow () returns a double . You may want to change your sum to type double .

If you don't mind using your own version, a better looking implementation, without using pow() will be

1. Store the existing value.
2. Multiply by x * x on each iteration
3. Take care of -ve sign for even numbered iteration.

Answer 2

First things first, your printf has the wrong format specifier for an int : use %d instead. But for non-integral x , you'll want to refactor to a double anyway, so %f will probably be retained.

Secondly, don't use pow : it will not be precise (probably implemented as exp(log) ) and you don't need to evaluate the power from scratch for each term.

Keep a running power: ie compute x * x * x initially, then successively multiply that by x * x for subsequent terms. Don't forget to alternate the signs: you can do that by multiplying by -1.

Answer 3

you are trying to find x^3,x^5 that is power in odd. so do a little change in your for loop. write this instead of your code. and if you give a large x or n value then it is preferable to declare sum as a long data type

#include<stdio.h>
#include<conio.h>
#include<math.h>
int main()
    {
        int x,n;
        long sum=0;
        printf("Length and Value");
        scanf("%d%d",&n,&x);

        for(int i=2;i<=n;i+=2)
        {
            sum+=(pow(x,i+1) * pow(-1,i));
        }
        printf("%l",sum);
        return 0;
    }

Answer 4

First of all, you are trying to evaluate a series that diverges for all points outside and on the circle of radius one (as a complex series). If you use an int for x, you will get each time values bigger and bigger, oscillating around 0. Try it with numbers of ||x|| < 1 ||x|| < 1 (this means double or float for x)

All the other answers posted are also usefull to get sooner to the expected value.