求阶乘
计算
e=1+1/1!+1/2!+1/3!+...+1/n!+...
误差小于给定误差限E=0.00005
[解决办法]

float sum = 1;
float temp = 1;
float k;
for(int idx = 1; ; idx++)
{
temp *= idx;
if(1/temp < 0.00005)
break;
sum += 1/temp;
}
cout<<sum<<endl;