Variance, Mode and Stadard Deviation

I´m in problems i don´t how to get Mode, Variance and Standard Deviation plss someone help me nad also i put (p); for no problems until ill can fix this, and idk why whrn i put the 30 intriger numbers the progma finishes :C someone help me

my code is this

include

using namespace std; int main () { int a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,y,z,aa,bb,cc,dd,ee,xx,ff,respuesta;

do{

cout<<endl<<"THIS PROGRAMME IS TO CALCULATE // MEAN // MEDIAN // MODE // DESVIACION ESTANDAR // VARIANZA of 30 INTRIGER NUMBERS"<<endl<<"Please enter Numbers"<<endl<<""    "";
cin>>a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,y,z,aa,bb,cc,dd,ee,ff,xx;
cout<<endl<<"PLEASE CHOOSE WHICH THING YOU WANT TO CALCULATE // (1) for MEAN // (2) for MEDIAN // (3) for MODE // (4) for STANDAR DEVIATION  // (5) VARIANCE // (6) for all Together "<<endl<<"PLEASE ENTER CATEGORY"<<endl<<""   "";
cin>>xx;


    switch (xx)
{
    case 1:
        cout<<"The result of Mean is --->"<<endl<<((a+b+c+d+e+f+g+h+i+j+k+l+m+n+o+p+q+r+s+t+u+v+w+y+z+aa+bb+cc+dd+ee,ff)/30);
        break;

    case 2:
        cout<<"The result of Median is --->"<<endl<<(p);

    case 3:
        cout<<"The result of Mode is -->"<<endl<<(p);

    case 4:
        cout<<"The result of Estandard Deviation is --->"<<endl<<(p);

    case 5:
        cout<<endl<<"The resul of Variance is -->"<<endl<<(p);

    case 6:
        cout<<endl<<"The Result of Mean is -->"<<endl<<((a+b+c+d+e+f+g+h+i+j+k+l+m+n+o+p+q+r+s+t+u+v+w+y+z+aa+bb+cc+dd+ee,ff)/30);

            cout<<endl<<"The Result of Median is --> "<<endl<<(p);

                cout<<endl<<"The Result of Mode is --->"<<endl<<(p);

                    cout<<endl<<"The Result of Estandard Variation is --->"<<endl<<(p);

                        cout<<endl<<"The result of Variance is -->"<<endl<<(p);

     }

cout<<endl<<"press 6 to continue or any letter to close this sesion";
cin>>respuesta;
    }while (respuesta !='6' );


return 0;

}

UNTIL THIS IS CORRECT BUT I DONT KNOW HOW TO GET THAT VARIANCE, STANDARD VARIATION AND MODE

AND WHR I TRIED TO PUT 30 NUMBERSA IDK WHY PROGRAM FINISHES :d someone hrlp me pls