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[Zrk2]

So, I've just started learning to program (I'm taking Intro to Programming) and I'm stuck on a question. I have to write a program that will solve for the voltage through a resistor for every value of temperature between 0 and 100, and print out the voltage for every temperature value that is a multiple of 10. The question reads as follows:

The resistor R represents a temperature sensor enclosed in the beaker. The resistance R, in
Ω, is related to the temperature T, in °C, by the equation
r=r₀+kt
where R₀ = 50 and k = 0.5.

The voltmeter displays the value of the voltage across the sensor
v_m=r*v_s/(r_s+r)

The voltage vm indicates the temperature, T, of the water according to the equation
t=150*v_m/(20-v_m)-100

Write a C++ program that prints a table showing the meter voltage corresponding to
water temperatures varying from 0 °C to 100 °C in increments of 10 degrees.

So far I've done this:

Spoiler: Code (click to show/hide)

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{
   double r, rnot=50, k=0.5, vs=20, rs=75, vm, t=0;
   r=rnot+k*t;
   vm=r*vs/(rs+r);
   t=150*vm/(20-vm)-100;
   do {
      if (t==0 || t==10 || t==20 || t==30 || t==40 || t==50 || t==60 || t==70 || t==80 || t==90 || t==100)
         cout<<"When t is "<<t*10<<"The voltage of the meter is "<<vm<<"."<<endl;
      t++;
   } while t<=10
}

I tried incrementing t nine more times in order to insure it reaches 10, but that gave me the same error compiling; syntax error: identifier "t."

[Dutchling]

C++ looks like someone made a language out of math. D:

[Max White]

Ok before I even start to look at that, your IF statement is fuck. Use the modulus operator instead.

Code: [Select]

if (t % 10 == 0)While you do that, I will bother to actually read the code.

[Putnam]

C++ looks like someone made a language out of math. D:

That's mostly because the variable names are ripped straight out of the equations involved If the variable names weren't so horribly obtuse and the code were commented, that wouldn't look so bad.

[Twiggie]

use a for loop instead of a while loop, and dont use a double for the counter (not sure if this will actually break anything, its just better practice to use ints if you dont explicitly need a double).

remove the initialisation of t that you already have and use

for(int t = 0; t < 101; t +=10) {

}

in place of the while loop. then get rid of that hideous if statement, and move the
 r=rnot+k*t;
   vm=r*vs/(rs+r);
   t=150*vm/(20-vm)-100;

inside the loop , before the  cout statement (since you want to recalculate the voltage of the meter every time you change the temperature)

[MorleyDev]

If the variable names weren't so horribly obtuse and the code were commented, that wouldn't look so bad.

If you're doing the former, you should have no need for the latter :-D if code needs comments to be understood it isn't very good code ;-)

[Zrk2]

I can't use the modulus function there, I get an error; it has to be an l-value. What if I wrote a separate variable for t%10? It appears to work.

I've updated and commented the code. At this point it compiles but prints nothing.

Spoiler: Still Code (click to show/hide)

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{
// The variables for the equations, some are cosntants others are not. r is the resistance of the resistor. rnot is the initial resistance. k is a dummy value dictated in the question. vs is the voltage of the resistor, and rs is the resistance of it. vm is the voltage of the meter.
   double r, rnot=50, k=0.5, vs=20, rs=75, vm;
// t is temperature. a is the "check value" to determine whether or not to print the values.
   int t, a;
   for(int t = 0; t < 101; t +=10) {
// The equations given in the question
      r=rnot+k*t;
      vm=r*vs/(rs+r);
      vm=(20*t+2000)/(250+t);
      a=t%10;
// The actual loop.
      if (a=0)
         cout<<"When t is "<<t<<"The voltage of the meter is "<<vm<<"."<<endl;
      t++;
      t++;
      t++;
      t++;
      t++;
      t++;
      t++;
      t++;
      t++;
      t++;
   }

   system("pause");
}

[Twiggie]

ok, just take out the t increments. you're incrementing t by 10 in the for loop (thats what the t += 10 does), so you dont need to do that. also that if statement is now irrelevant since t will always be 10*x (since you're incrementing it by 10 starting from 0) and so t%10 will always be 0.

you also have a double declaration of t.

EDIT: I started hyperventilating when i saw all those t++s -.-

[Max White]

I'm... Not fully convinced you have a full and working understanding of how loops work.
Get rid of all of those t++ statements as well as the if (a=0) and the first t declaration.

Damn ninjas.

[Putnam]

Damn ninjas indeed.

[Zrk2]

I'm... Not fully convinced you have a full and working understanding of how loops work.
Get rid of all of those t++ statements as well as the if (a=0) and the first t declaration.

Damn ninjas.

Not really. They were introduced last week and this is my first real experience with them.

[Max White]

You should start a bit more simple with playing with them before you go all out then.
Make a program that prints the numbers from 1 to 10.

[Putnam]

http://cplusplus.com/doc/tutorial/control/

>_>

[MagmaMcFry]

How much are we allowed to help you?

Spoiler: Commented solution (click to show/hide)

Code: [Select]

#include <iostream>

using namespace std;

int main() {
    int t;
    for (t = 0; t <= 100; t += 10) {                // Start by setting t = 0. Now repeat the code in the braces as long as t <= 100, doing t += 10 after every run of the braced code.
                                                    // This ensures that the braced code will be run once each for t from 0 to 100 in increments of 10.

        double vm = 20 * (t + 100) / (t + 250.0);   // This is what you get when you solve t=150vm/(20-vm)-100 for vm. The rest of your assignment is only there to confuse you.

        cout << "When the temperature is " << t << "°C, the voltage of the meter is " << vm << "V." << endl;
    }
}


[Zrk2]

How much are we allowed to help you?

Spoiler: Commented solution (click to show/hide)

Code: [Select]

#include <iostream>

using namespace std;

int main() {
    int t;
    for (t = 0; t <= 100; t += 10) {                // Start by setting t = 0. Now repeat the code in the braces as long as t <= 100, doing t += 10 after every run of the braced code.
                                                    // This ensures that the braced code will be run once each for t from 0 to 100 in increments of 10.

        double vm = 20 * (t + 100) / (t + 250.0);   // This is what you get when you solve t=150vm/(20-vm)-100 for vm. The rest of your assignment is only there to confuse you.

        cout << "When the temperature is " << t << "°C, the voltage of the meter is " << vm << "V." << endl;
    }
}


I don't know, but I managed to fix it. If anyone cares to take a look at my solution, here it is:

Spoiler: This One Actually Works (click to show/hide)

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{
// The variables for the equations, some are cosntants others are not. r is the resistance of the resistor. rnot is the initial resistance. k is a dummy value dictated in the question. vs is the voltage of the resistor, and rs is the resistance of it. vm is the voltage of the meter.
   double r, rnot=50, k=0.5, vs=20, rs=75, vm;
// t is temperature.
   double t=0;
   do {
// The equations given in the question
      r=rnot+k*t;
      vm=r*vs/(rs+r);
      vm=(20*t+2000)/(250+t);
// The actual loop.
         cout<<"When t is "<<t<<" The voltage of the meter is "<<vm<<"."<<endl;
      t=t+10;
   } while (t!=110);

   system("pause");
}