#include <stdio.h>
int main(){


    //用while循环求 1-1/2+1/3-1/4+1/5-1/6+........-1/100 的和


    double i=1 ,sum=0;

    int n=1;
   
   

    do{
        if("n % 2  == 1")
        sum =sum+1/i;
        
   
 else
   
     
        sum =sum-1/i;
        n++;i++;
    }
   
    while(n <= 100);
   
    printf("%lf\n",sum);


   
    return 0;




}

if("n % 2  == 1")//这个...

还是5.多啊，怎么改，老哥

#include <stdio.h>
int main(){
    //用while循环求 1-1/2+1/3-1/4+1/5-1/6+........-1/100 的和
    double i=1 ,sum=0;
    int n=1; 
    do{ 
        if(n%2==1)
        sum =sum+1/i;                 

 else  
        sum =sum-1/i;
        n++;
        i++;
    }    
    while(n <= 100);    
    printf("%lf\n",sum);
    return 0;
}[local]1[/local]

#include <stdio.h>
int main(){

//用while循环求 1-1/2+1/3-1/4+1/5-1/6+........-1/100 的和
    double sum=0;
    int n=1;
   
     do{
        if( n % 2  == 1 )
           sum = sum + 1.0 /n;
         else
           sum = sum - 1.0 /n;
        n++;
    } while(n <= 100);
   
    printf("%lf\n",sum);
    return 0;

}

if("n % 2  == 1")

代码给你，你照打，都能出错呀！！！
"n % 2  == 1"
带个""  干嘛？？？  

细心细心