Gas law C++ please helppppp asap

[sjabat]

please check what is wrong help please please
i need do and while in the program if the user inputs negative the output will be invalid

#include <iostream>
#include <cctype>
#include <windows.h>
using namespace std;
int main ()
{
int n,p,v,t, ctr;
char again,A,B,C,letter;

cout<<"(A) TO find pressure: \n (B) To find volume: \n (C) To find Temperature: "<< endl;
cin>>letter;
if (letter==A)
do{
if(!(p == 0))
cout<<"input value of number of moles"<<endl;
cin>>n;
cout<<"input value of temperature."<<endl;
cin>>t;
cout<<"input value of Volume"<<endl;
cin>>v;
cout<<"the value of Pressure="<<p<<endl;
}while ((!letter == A));
p=(n*0.0821*t)/v;

else if (letter==B)
do {cout<<"input value of number of moles"<<endl;
cin>>n;
cout<<"input value of temperature."<<endl;
cin>>t;
cout<<"input value of Pressure"<<endl;
cin>>p;
v=(n*0.0821*t)/p;
cout<<"the value of volume="<<v<<endl;
}while (!(letter == B));

else if (letter==C)
do {cout<<"input value of number of moles"<<endl;
cin>>n;
cout<<"input value of Pressure."<<endl;
cin>>p;
cout<<"input value of Volume"<<endl;
cin>>v;
t=(p*v)/(0.0821*n);
cout<<"the value of temperature="<<t<<endl;
}while ((!letter == C));

return 0;
}

[letscode]

Please use the code tags for posting code.

Use double type for p,v,t,n. Also why should you use !(p==0) simply use p!=0.

Any number is negative if it is less than zero. So simply check

if(v<0)
{
      cout<<"invalid input";
}

Do it for every input.

[Stewbond]

Here's your main issue:

int n,p,v,t, ctr;
char again,A,B,C,letter;

// ...
do{
  if(!(p == 0))
    cout<<"input value of number of moles"<<endl;
  cin>>n;
  cout<<"input value of temperature."<<endl;
  cin>>t;
  cout<<"input value of Volume"<<endl;
  cin>>v;
  cout<<"the value of Pressure="<<p<<endl;
}while ((!letter == A));

First, p is not initialized so you don't know if it will be 0 or not.
Second You need { } around all of those cout/cins. Otherwise, only line 7 above is inside of the if

Third, you need { } around each if(letter == 'A') block.

Fourth, n,p,v,t, are all ints, make them doubles.

Fifth: A/B/C aren't initialized to a value. I assume you wanted letter == 'A'

I'll post some updated code in a moment to try.

[Stewbond]

Try this. I still see some significant issues and can give you some pointers on that. But see if you can figure it out first.

#include <iostream>
//#include <cctype> not needed
//#include <windows.h> not needed
using namespace std;

int main ()
{
    double n,p,v,t;
    char letter;

    cout<<"(A) TO find pressure: \n (B) To find volume: \n (C) To find Temperature: "<< endl;
    cin>>letter;

    if (letter=='A') // Could use a switch statement here
    {
        do
        {
            if(!(p == 0)) // What do you think p is now?
            {
                cout<<"input value of number of moles"<<endl;
                cin>>n;
                cout<<"input value of temperature."<<endl;
                cin>>t;
                cout<<"input value of Volume"<<endl;
                cin>>v;
                cout<<"the value of Pressure="<<p<<endl; // P isn't calculated yet!
            }
        }while ((!letter == 'A')); // Of course letter == 'A', That's why we're in the if statement
        p=(n*0.0821*t)/v; 
    }
    else if (letter=='B')
    {
        do
        {
            cout<<"input value of number of moles"<<endl;
            cin>>n;
            cout<<"input value of temperature."<<endl;
            cin>>t;
            cout<<"input value of Pressure"<<endl;
            cin>>p;
            v=(n*0.0821*t)/p;
            cout<<"the value of volume="<<v<<endl;
        }while (!(letter == 'B'));
    }
    else if (letter=='C')
    {
        do
        {
            cout<<"input value of number of moles"<<endl;
            cin>>n;
            cout<<"input value of Pressure."<<endl;
            cin>>p;
            cout<<"input value of Volume"<<endl;
            cin>>v;
            t=(p*v)/(0.0821*n);
            cout<<"the value of temperature="<<t<<endl;
        }while ((!letter == 'C'));
    }
    return 0;
}

[Stewbond]

I think this one is a working solution. I put everything into one big do loop. The only thing that isn't in there is a message telling you that you've entered an invalid input.

#include <iostream>
using namespace std;

int main ()
{
    double n,p,v,t;
    char letter, again;

    do
    {
        do
        {
            cout<<"(A) To find pressure: \n(B) To find volume: \n(C) To find Temperature: "<< endl;
            cin>>letter;
        } while (letter != 'A' && letter != 'B' && letter != 'C');

        if (letter != 'A')
        {
            do
            {
                cout<<"input value of Pressure"<<endl;
                cin>>p;
            } while (p <= 0);
        }
        if (letter != 'B')
        {
            cout<<"input value of Volume"<<endl;
            cin>>v;
        }
        if (letter != 'C')
        {
            cout<<"input value of Temperature."<<endl;
            cin>>t;
        }

        cout<<"input value of number of Moles"<<endl;
        cin>>n;

        if (letter=='A')
        {
            p=(n*0.0821*t)/v;
            cout<<"the value of Pressure="<<p<<endl;
        }
        else if (letter=='B')
        {
            v=(n*0.0821*t)/p;
            cout<<"the value of Volume="<<v<<endl;
        }
        else if (letter=='C')
        {
            t=(p*v)/(0.0821*n);
            cout<<"the value of Temperature="<<t<<endl;
        }

        cout << "do you want to go again? (Y/n): ";
        cin >> again;
    }while (again != 'n' && again != 'N');
    return 0;
}

[sjabat]

THANK YOU THIS A GREAT BIG HELP SRSLY THIS IS FOR MY PROJECT THANK YOU THANK YOU

[sjabat]

kindly please check this. there is something wrong if i press Y the output is invalid input but it should be returning back to the main choices like "To find pressure etc...

if (letter != 'A')
{
do
{
cout<<"input value of Pressure"<<endl;
cin>>p;

do{
if (p<0)
{
cout<<"invalid input"<<endl;
}
cout << "do you want to go again? (Y/n): ";
cin >> again;
}while (again != 'n' && again != 'N');

} while (p <= 0);

[mutexe]

you've been asked to use code tags, but you seem not to want to..

and stewbond's solution work's fine for me.

[sjabat]

please correct my work

if the user inputs negative it the output will be invalid input

[Stewbond]

You wanted to use do-while, but I'd rather use while. If you want to display "invalid input" change this:

do
{
    cout<<"input value of Pressure"<<endl;
    cin>>p;
} while (p <= 0);

to this:

while (true)
{
    cout<<"input value of Pressure"<<endl;
    cin>>p;

    if (p > 0) break;

    cout << "Invalid Input" << endl;
}

[sjabat]

is there another way for break bcoz our teacher havent yet taught us the break/case/switch

[Stewbond]

There's always another way...

do
{
    cout<<"input value of Pressure"<<endl;
    cin>>p;

    if (p <= 0) 
        cout << "Invalid Input" << endl;
} while ( p <= 0 );

But in this case you have the conditional statement twice, so it's not as elegant.

[sjabat]

oh i see. please check this. please correct my mistakes
i tried to put (t<=0) but when i executed it everytime i put negative number and after i correct it into postive it still resulted to "please enter a non negative number


#include <iostream>
#include <windows.h>
using namespace std;

int main ()
{

double n,p,v,t;
char letter, again;

do{
system("cls");
do
{
cout<<"GAS LAW SOLVER"<<endl;
cout<<"******************************\n**PLEASE CHOOSE YOUR PROBLEM**\n** (A) To find pressure: **\n** (B) To find volume: **\n**(C) To find Temperature: **\n**(D) To find Number of Moles **\n******************************"<< endl;
cin>>letter;
letter=toupper(letter);
if (letter!='A' && letter!='B' && letter!='C' && letter!='D')
cout<<endl<<endl<<"INVALID INPUT!"<<endl<<endl;
} while (letter !='A' && letter !='B' && letter != 'C' && letter != 'D');

if (letter != 'A')
{

do{
cout<<"input value of Pressure"<<endl;
cin>>p;

if (p <= 0)
cout << "Invalid Input" << endl;
} while ( p <= 0 );
}

if (letter != 'B')
{

do{
cout<<"input value of Volume:"<<endl;
cin>>v;

if (v<=0)
cout << "Invalid Input" << endl;
cout<<"\n**Please enter a non negative number for pressure to proceed**\n"<<endl<<endl;
}while (v<=0);

}


if (letter != 'C')
{
do{
cout<<"input value of Temperature."<<endl;
cin>>t;

if (t<=0)
cout<< "Invalid Input"<<endl;
cout<<"\n**Please enter a non negative number for pressure to proceed**\n"<<endl<<endl;
}while (t<=0);
}


if (letter != 'D')
{

do{
cout<<"input value of number of Moles"<<endl;
cin>>n;

if (n<=0)

cout << "Invalid Input" << endl;
cout<<"\n**Please enter a non negative number for pressure to proceed**\n"<<endl<<endl;
}while (n<=0);
}


if (letter=='A')
{
p=(n*0.0821*t)/v;
cout<<"the value of Pressure="<<p<<endl;
}
else if (letter=='B')
{
v=(n*0.0821*t)/p;
cout<<"the value of Volume="<<v<<endl;
}
else if (letter=='C')
{
t=(p*v)/(0.0821*n);
cout<<"the value of Temperature="<<t<<endl;
}
else if (letter=='D')
{
n=(p*v)/(0.0821*t);
cout<<"the value of Moles="<<n<<endl;
}

cout << "do you want to go again? (Y/n): ";
cin >> again;
}while (again != 'n' && again != 'N');

return 0;
}

[sjabat]

please correct all the mistakes ive done. i have to make flowchart for this. this project will be submitted on wednesday huhu. :))