Ошибка error C3861: erfc: идентификатор не найден

#include<iostream>
#include<fstream>
#include<math.h>
 
using namespace std;
 
int main()
{
    ifstream file;
    file.open("outb.txt");
 
    char t[2];
    int n=0,one=0,V=0,i=0;
    float Sn=0,pi=0,tau;
    while(!file.eof())
    {
        file>>t[0];
        if(t[0]=='1') one++;
        if(t[0]=='-') continue;
        Sn=Sn+2*(t[0]-48)-1;
        n++;
    }
    file.close();
    file.open("outb.txt");
    tau=2/sqrt(n);
    pi=(float)one/n;
    if(fabs(pi-0.5)<tau)
    {
        file>>t[0];
        while(!file.eof())
        {
             file>>t[1];
             if (t[0]!=t[1]) V=V+1;
             t[0]=t[1];
        }
    }
    Sn=fabs(Sn)/sqrt(n);
    cout<<"Frequency Test. p="<<erfc(Sn/sqrt(2))<<endl;
    cout<<"Runs Test. p="<<erfc(fabs(V-2*pi*n*(1-pi))/(2*sqrt(2*n)*pi*(1-pi)))<<endl;
    file.close();
    return 0;

static const double rel_error= 1E-12;        //calculate 12 significant figures
//you can adjust rel_error to trade off between accuracy and speed
//but don't ask for > 15 figures (assuming usual 52 bit mantissa in a double)
 
double erfc(double x)
//erfc(x) = 2/sqrt(pi)*integral(exp(-t^2),t,x,inf)
//        = exp(-x^2)/sqrt(pi) * [1/x+ (1/2)/x+ (2/2)/x+ (3/2)/x+ (4/2)/x+ ...]
//        = 1-erf(x)
//expression inside [] is a continued fraction so '+' means add to denominator only
{
    static const double one_sqrtpi=  0.564189583547756287;        // 1/sqrt(pi)
    if (fabs(x) < 2.2) {
        return 1.0 - erf(x);        //use series when fabs(x) < 2.2
    }
    if (signbit(x)) {               //continued fraction only valid for x>0
        return 2.0 - erfc(-x);
    }
    double a=1, b=x;                //last two convergent numerators
    double c=x, d=x*x+0.5;          //last two convergent denominators
    double q1, q2= b/d;             //last two convergents (a/c and b/d)
    double n= 1.0, t;
    do {
        t= a*n+b*x;
        a= b;
        b= t;
        t= c*n+d*x;
        c= d;
        d= t;
        n+= 0.5;
        q1= q2;
        q2= b/d;
      } while (fabs(q1-q2)/q2 > rel_error);
    return one_sqrtpi*exp(-x*x)*q2;
}