Exercise 2-15 Find the sum of the first N items in a simple interleaved sequence (15 points)
This question requires writing a program to calculate the sum of the first N items in the sequence 1-1/4 + 1/7-1/10 + ….
Input format:
Input gives a positive integer N in one line.
Output format:
output the partial sum value S in the format of "sum = S" in one line, accurate to three decimal places. The title guarantees that the calculation result does not exceed the double precision range.
Input example:
10
Output example:
sum = 0.819
Author
C course group
Unit
Zhejiang University
Code length limit
16 KB
Time limit
400 ms
Memory limit
64 MB
#include <stdio.h>
#include <math.h>
int main() {
int n, i, d = 1;
double sum = 0;
if (scanf("%d", &n) == 1) {
for (i = 1; i <= n; i++) {
sum += pow(-1, i + 1) * 1.0 / d;
d += 3;
}
printf("sum = %.3f", sum);
}
return 0;
}