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#include<stdio.h>
void main()
{
 float sum=1;
 int i=1;
 long int jiecheng=1;
 do{
     sum+=1.0/jiecheng;
     i++;
     jiecheng=jiecheng*i;
    }while((1.0/jiecheng)>1e-6);
 printf("i=%d,sum=%f\n",i,sum);
}

结果是：i=10,sum=2.718282

#include<stdio.h>
#include<math.h>
void main()
{
    int factorial(int);
    int i;
    float sum=1.0;
    for(i=1;(1/(float)fabs(factorial(i)))>1e-6;i++)
        sum=sum+1/(float)factorial(i);
    printf("%f",sum);
}
int factorial(int x)
{
    int a=1;
    for(;x>0;)
        a=a*x--;
    return(a);
}

算出2.718282

不错