Hello again.

I hope everyone is well.

I am still having a few issues. I am still having a few issues getting this program going. I have put the encryption program below. I am just not sure how to use this program. So I'm hoping someone could give me some pointers.

Thanks in advance.

Code:
double ran2(int &idum)
{
	const int IM1=2147483563, IM2=2147483399;
	const int IA1=40014, IA2=40692, IQ1=53668, IQ2=52774;
	const int IR1=12211, IR2=3791, NTAB=32, IMM1 = IM1-1;
	const int NDIV=1+IMM1/NTAB;
	const double EPS=3.0e-16, RNMX=1.0-EPS, AM1.0/(double)(IM1);
	static int idum2=123456789, iy=0;
	static int iv[NTAB];
	int j,k;
	double temp;

	if (idum <= 0)
	{
		idum=(idum==0 ? 1 : -idum);
		idum2=idum;
		for (j=NTAB+7; j>=0; j--){
			idum=IA1*(idum-k*IQ1)-k*IR1;
			if (idum<0) idum += IM1;
			if (j<NYAB) iv[j] = idum;
		}
		iy=iv[0];
	}
	k=idum/IQ1;
	idum=IA1*(idum-k*IQ1)-k*IR1;
	if(idum<0) idum += IM1;
	k=idum2/IQ2;
	idum2=IA2*(idum2-k*IQ2)-k*IR2;
	if(idum2<0) idum2 += IM2;
	j=iy/NDIV;
	iy=iv[j]-idum2;
	iv[j]=idum;
	if(iy<1)iy += IMM1;
	if((temp=AM*iy)>RNMX) return RNMX;
	else return temp;
}