这个C语言多项式就和问题，精确度不是太会。为啥就相差0.000512。请详细说明

改用double
调整计算顺序，不要先乘再除，尽量避免乘除法的精度损失

 #include <iostream>

using namespace std;

double f1(int n)
{
    double r = 1;
    for (int i = 2; i <= n; i++)
        r *= (double)i;
    return r;
}

double f2(double x, int n)
{
    double r = 1;
    for (int i = 1; i <= n; i++)
        r *= x;
    return r;
}

double f3(int n, double x)
{
    double u = 0.5;
    for (int i = 1; i < n; i++)
    {
        u *= (0.5 - i);
    }
    return u * f2(x, n) / f1(n);
}

int main()
{
    double ps = 1;
    double x = 0.21;
    int n = 1;
    while (1)
    {
        double s = ps + f3(n, x);
        if (abs(s - ps) < 0.000001) break;
        ps = s;
    }
    cout << ps << endl;
}

你没有贴你的代码出来，怎么让人分析你的问题呢？