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

#include<stdio.h>

int main() {
  int temp = 1;//用来代表正负号
  double sum = 0;//double类型
  for (int i = 1; i <101; i++) {
    sum = temp*(1.0 / i )+ sum;
    temp = -temp;   //先加后减
  }
  printf("%lf", sum);//双精度浮点型
  return 0;
}

单精度浮点型：%f

双精度浮点型：%lf