#include<iostream>
 
#include<string>
void menu();
 
using namespace std;
char choice;
 
void digcom ();
 
void matrices ();
 
int main ()
 
{ menu();
 
 
 
return 0;
 
}
void menu()
{
cout<<"\tMENU" <<endl<<"MATHEMATICS(matrices select A)\n"<<"DIGITAL COMMS select B\n"<<"c TO EXIT"<<endl;
 
cin>>choice;
 
while(choice!='c')
{
 
switch(choice)
 
{
 
case ('A') : matrices();break;
 
case ('B'): digcom();break;
 
default:cout<<"re-enter\n";
cin>>choice;break;
 
}
}
}// end of menu
 
void digcom()
 
{
 
 string ans;
 
 int *score;
 
 score=new int;  // dynamic memory allocation
 
 if(score==NULL)
 
 {
 
 cerr<<"insufitient space could not allocate memory"<<endl;
 
 exit(1);
 
 }
 
string questions[10]={"State the basic form of representation of a image","What does LAN stand for","What type of data transmission allows data to only flow in one direction","in a wireless network data is transmitted at the speed of __","which is___","determine the propagation delay associated with a connectionless communication channel through a private telephone network","What does modem stand for","what does IP stand for","what format is used to store data"};
 
string answers[10]={"pixels","Local Area Network","simplex","light,5*10^-8","5*10^-6","modulator-demodulator","Internet Protocol","digital format"};
 
string store[10];
 
cout<<"MAKE SURE THAT UR ANSWERS ARE IN SMALL LETTER UNLESS STATING THE ABBREVIATION"<<endl;
 
*score=0;
 
for(int n=0;n<9;n++)
 
{
 
cout<<questions[n]<<endl;
 
getline(cin,ans);
 
int f=ans.length();
 
store[n]=ans.substr(0,f);   // string function
 
}
 
for(int i=0;i<10;i++)
 
{
 
if(answers[i]==store[i])
 
{
 
*score++;  // pointer is incremented   possible use before definition
 
}
 
}
 
cout<<"you got "<<*score<<"/10"<<endl;
 
delete score;
 
 
menu();
 
} // end of this function
 
 
 
void matrices() // new function
{
 
int q1[4],q2[4],q3[4];
float da,dx,dy,dz,x,y,z,*ptr2;;
cout<<"\nTHE EQUATION MUST BE ENTERED USING CO-OEFICIENTS ONLY"<<endl
    <<"ENTER EQUATION 1"<<endl;
  for(int a=0;a<=3;a++)
    {
      cin>>q1[a];
    }
 
cout<<"\nEQUATION 1 COMPLETE, ENTER EQUATION 2"<<endl;
 
 for(int b=0;b<=3;b++)
   {
    cin>>q2[b];
   }
 
cout<<"\nEQUATION 2 COMPLETE, ENETR EQUATION3"<<endl;
 for(int c=0;c<=3;c++)
   {
    cin>>q3[c];
   }
int d,e,f,*pointer1;
// DET A
   pointer1=q1;
   d=*pointer1*((q2[1]*q3[2])-(q3[1]*q2[2]));
   pointer1++;
   e=*pointer1*((q2[0]*q3[2])-(q3[0]*q2[2]));
   pointer1++;
   f=*pointer1*((q2[0]*q3[1])-(q3[0]*q2[1]));
   pointer1++;
   da=d-e+f;
 
//DET X
   d=*pointer1*((q2[1]*q3[2])-(q3[1]*q2[2]));
   pointer1-=2;
   e=*pointer1*((q2[3]*q3[2])-(q3[3]*q2[2]));
   pointer1++;
   f=*pointer1*((q2[3]*q3[1])-(q3[3]*q2[1]));
   dx=d-e+f;
 
//DET Y
   pointer1=q1;
   d=*pointer1*((q2[3]*q3[2])-(q3[3]*q2[2]));
   pointer1+=3;
   e=*pointer1*((q2[0]*q3[2])-(q3[0]*q2[2]));
   pointer1--;
   f=*pointer1*((q2[0]*q3[3])-(q3[0]*q2[3]));
   dy=d-e+f;
 
//DET Z
   pointer1=q1;
   d=*pointer1*((q2[1]*q3[3])-(q3[1]*q2[3]));
   pointer1++;
   e=*pointer1*((q2[0]*q3[3])-(q3[0]*q2[3]));
   pointer1+=2;
   f=*pointer1*((q2[0]*q3[1])-(q3[0]*q2[1]));
   dz=d-e+f;
 
 
float t[3];
t[0]=dx/da;
t[1]=dy/da;
t[2]=dz/da;
 
 
cout<<"\n...........OPTIONS........."<<endl
    <<"1. CALCULATE THE VALUE OF X"<<endl
    <<"2. CALCULATE THE VALUE OF Y"<<endl
    <<"3. CALCULATE THE VALUE OF Z"<<endl
    <<"4. CALCULATE ALL THE VALUES"<<endl
    <<endl<<"ENTER YOUR CHOICE"<<endl;
cin>>d;
 
if(d==4)
 {
  ptr2=t;
  cout<<"THE VALUE OF X IS: "<<*ptr2<<endl;
  ptr2++;
  cout<<"THE VALUE OF Y IS: "<<*ptr2<<endl;
  ptr2++;
  cout<<"THE VALUE OF Z IS: "<<*ptr2<<endl;
 }
 
  else
   {
    cout<<"THE VALUE IS: "<<t[d-1]<<endl;
   }
menu();
}