1-1/2+1/3-1/4...-1/100

#include<stdio.h>

int main() {
  int temp = 1;
  double sum = 0;
  for (int i = 1; i <101; i++) {
    sum = temp*1.0 / i + sum;
    temp = -temp;
  }
  printf("%lf", sum);
  return 0;
}