请你帮帮我解一下这道题吧

#include<stdio.h>
int main()
{
 int c,n;
 float b=0.0,m=1.0;
 while(m<=100)
 {
  if(((int)(m)+1)%2==0)
  {b=b+1/m;
  m=m+1;}
  else
  {b=b-1/m;
  m=m+1;}
 }
  printf("%f",b);
 return 0;
}

供参考：

#include <stdio.h>
int main()
{
    int i = 1, k = -1;
    float s = 0;
    while (i <= 100) 
    {
        k = -k;
        s += 1.0 * k / i;
        i++;
    }
    printf("%f", s);
    return 0;
}

 
#include<stdio.h>
int main ()
{
float sum=0;
int i=1;
while (i<=100){
  if (i%2==0) sum-=(1.0/i);
  else sum+=(1.0/i);
  ++i;
}
printf("%f",sum);
}