I was required to create a program with a function that changes height in feet to height in meters. I made the function and when I cout from the function I get the right value but when I cout it in main I get "nan". I dont understand why the value is not printing. This is my first time using this website so I am sorry if I miss anything.
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
double heightInMeters(double feet , double inches)
{
double footToMeter = 0.305;
double inchToMeter = 0.0254;
double heightInMeters = ((footToMeter * feet) + (inchToMeter * inches));
cout << heightInMeters << endl;
}
int main()
{
double feet, inches, calcheight;
char ch;
cout << "Enter your height [Use format ft-in]: ";
cin >> feet >> ch >> inches;
calcheight = heightInMeters(feet, inches);
cout << calcheight << endl;
return 0;
}
This function here:
double heightInMeters(double feet , double inches)
{
double footToMeter = 0.305;
double inchToMeter = 0.0254;
double heightInMeters = ((footToMeter * feet) + (inchToMeter * inches));
cout << heightInMeters << endl;
}
isn't returning anything. That's undefined behavior, what you get here
calcheight = heightInMeters(feet, inches);
Is most likely just some invalid rubbish value then. Perhaps instead of this:
cout << heightInMeters << endl;
You wanted this:
return heightInMeters;
Does your compiler issue any warnings for your code? If not, please try to find out if you can set it to give you more warnings. Most compilers usually complain about missing returns.
heightInMeters doesn't have an explicit return value.
Therefore, since it's not a void function (or main), the behaviour of your program is undefined.
Didn't your compiler warn you of that? It's an easy spot for a compiler to make in your case, and the current crop of compilers all warn if you turn the warning level up appropriately.
(Granted, NaN is a peculiar manifestation of that undefined behaviour.)
Finally, note that one foot is exactly 0.3048 meters. Base your conversion metrics from that. Your values introduce unnecessary imprecision.
void f()
{
double a=0.3;
cout << a << endl;
}
//
// inside main function
f();
double f()
{
double a=0.3;
return a；
}
// inside main function
cout << f() << endl;
Because the return value of your code is not specified, the output is “nan“
Related
Hi I am working on a project for school and cannot for the life of me figure out how to get the totalJobCost function to work. The other functions work without a problem but i don't think they are passing the var back to main for totalJobCost to grab as the totalJobCost outputs 0. here is the code that i am using:
#include "stdafx.h"
#include <iostream>
using namespace std;
void space(double paintarea, double paintcost, double paintneeded, double totalpaint);
void cost(double hrs, double hrcost, double spacetopaint);
void totalJobCost(double allTheirPaintCost, double allTheirWages, double theirTotalJobCost);
const double AREA_FORMULA = 220.00;
const double AREAFORMULA_PAINT = 1.00;
const double AREAFORMULA_HOURS = 8.00;
const double AREAFORMULAHOURS_WAGES = 35.00;
int main()
{
double areaTP;
double paintCST = 0;
double paintNeeded = 0;
double allPaintCost = 0;
double hoursNeeded = 0;
double hoursWages = 0;
double allWages = 0;
double allJobCost = 0;
cout << "Enter the square footage you need to paint, then press enter" << endl;
cin >> areaTP;
cout << "Enter the price by gallons of paint you will use, then press enter" << endl;
cin >> paintCST;
while (paintCST < 10)
{
cout << "Enter the price by gallons of paint you will use, then press enter. cannot be less than 10 :";
cin >> paintCST;
}
space(areaTP, paintCST, paintNeeded, allPaintCost);
cost(hoursNeeded, hoursWages, areaTP);
totalJobCost(allPaintCost, hoursWages, allJobCost);
system("Pause");
return 0;
}
void space(double paintarea, double paintcost, double paintneeded, double totalpaint)
{
paintneeded = paintarea / AREA_FORMULA * AREAFORMULA_PAINT;
totalpaint = paintneeded * paintcost;
cout << "How many gallons of paint you will need: " << paintneeded << endl;
cout << "Your total paint cost will be: " << totalpaint << endl;
}
void cost(double hrs, double hrcost, double spacetopaint)
{
hrs = (spacetopaint / AREA_FORMULA) * AREAFORMULA_HOURS;
hrcost = hrs * AREAFORMULAHOURS_WAGES;
cout << "The number of hours for the job will be: " << hrs << endl;
cout << "The total amount of wages will be: " << hrcost << endl;
}
void totalJobCost(double totalpaint, double hrcost, double theirTotalJobCost)
{
theirTotalJobCost = totalpaint + hrcost;
cout << "The total price of your paint job will be: " << theirTotalJobCost << endl;
}
You need to declare your arguments (totalpaint and hrcost) as references.
Currently, functions space() and cost() just make copies of totalpaint and hrcost when called, update them, then print them. But when the functions return, the values stored in totalpaint and hrcost are lost.
To fix this, you should declare those functions as follows:
void space(double paintarea, double paintcost, double paintneeded, double& totalpaint)
void cost(double hrs, double& hrcost, double spacetopaint)
Now whatever variable you pass in as totalpaint or hrcost will be updated when space() or cost() operates on it.
This is a pass by value vs. pass by reference issue.
In C++, booleans, characters, integer numbers, floating-point numbers,
arrays, classes—including strings, lists, dictionaries, sets, stacks,
queues—and enumerations are value types, while references and pointers
are reference types.
CPP reference
The variables you are using are doubles (double precision floating point), so they are value types. When you pass value type variables to functions as parameters, the current value of the variables is copied to the calling stack of the function you called. Once inside the function, the parameter names are just names you use to access the copied values. Whatever you do to these copied values will not affect the value of the original variables you passed to the function. Read up on function scope and the calling stack architecture of C/C++ to understand more.
To change the value of a variable across function calls, you need to pass a reference to its location in memory. If you declare a variable in the first few lines of a function, its location in memory will be part of that function’s call stack, and you can safely access that memory in any function calls that are called within the original function. So you can do this:
int main() {
double variable = 0;
function(&variable);
cout << variable;
}
void function(double* variable_address) {
*variable_address = 1.5;
}
This involves the dereference operator. Sorry if this is too much info, but pass by reference and pass by value are easier to understand if you know what’s happening in the underlying function call and memory architecture of C/C++.
I'm trying to get an output for my weight_Fee using double, and I cannot seem to get the correct value. I have tried using float, but I haven't been able to get that to work either.
My goal is to get an output value containing two decimal places as if I were to be calculating a cost, but I get 0.00 every time.
I'm new to C++, so if anyone can tell me what I'm doing wrong, it would be a big help. Thanks.
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
using namespace std;
int main() {
double animal_Weight;
double weight_Fee = .5 * animal_Weight;
cout << "In rounded poundage, how much does your animal weigh? ";
cin >> animal_Weight;
cout << setprecision (2) << fixed << weight_Fee;
return 0;
}
double weight_Fee = 0.5 * animal_Weight;
When you initialize weight_Fee like that you are setting it equal to 0.5 * the current value of animal_Weight. Since this is currently undefined weight_Fee will be some garbage value.
When you set animal_Weight to something based on user input later on, that won't change the value of a previous variable. You'll have to use that statement again to set weight_Fee = 0.5 * the current value of animal_Weight
The best thing to do is probably to just declare weight_Fee at the top, and not define it until you have set animal_Weight to what you want it to be.
Something like this:
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
using namespace std;
int main() {
double animal_Weight;
double weight_Fee;
cout << "In rounded poundage, how much does your animal weigh? ";
cin >> animal_Weight;
weight_Fee = .5 * animal_Weight
cout << setprecision (2) << fixed << weight_Fee;
return 0;
}
The variable animal_Weight is undefined and can be initialized to anything by the compiler or the operating system or whatever value happen to be last in the memory.
You need to calculate weight_Fee after you input a value for animal_Weight:
double animal_Weight = -1.0;
cout << "In rounded poundage, how much does your animal weigh? ";
cin >> animal_Weight;
double weight_Fee = .5 * animal_Weight;
cout << setprecision (2) << fixed << weight_Fee;
Either someone forgot to mention to you that your computer does only 1 instruction at a time (and the C++ compiler generates instructions in a sequence corresponding to your code); or perhaps you've never grok'ed the statement.
1) double animal_Weight;
2) double weight_Fee = .5 * animal_Weight;
3) cout << "In rounded poundage, how much does your animal weigh? ";
4) cin >> animal_Weight;
5) cout << setprecision (2) << fixed << weight_Fee;
Your code prompts for (3) and cin's (4) an animal weight. ok.
But the weight_Fee was computed (2) prior to knowing the animal_Weight (4). This is a logic error.
So if the computation at (2) did not know the animal_Weight, the correct value simply can not be determined.
Also, the animal_Weight (1) is not initialized, creating undefined behaviour.
Note that you CAN get the compiler to complain about (generate a warning) the attempted use of an uninitialized variable (at line 2), but you have to command the compiler to do so (by using an option).
I am required to fully understand the following code :
#include <iostream>
using namespace std;
double area(double length, double width);
double time(double p_area, double h_area, double mow_rate);
int main() {
double d_plot_length, d_plot_width, d_home_side, d_mow_rate;
double plot_area, home_area, time_taken;
// I've used double for all of these to get the most precise values possible, something I'd only really consider doing on small programmes such as this
cout << "What is the length of the plot? In meters please." << endl;
cin >> d_plot_length;
cout << "What is the width of the plot? In meters please." << endl;
cin >> d_plot_width;
cout<< "What is the size of the side of the house? In meters please." << endl;
cin >> d_home_side;
cout << "What is the rate at which you are going to be mowing? In meters per minute please" << endl;
cin >> d_mow_rate;
// Just getting all the data I need from the user
plot_area = area(d_plot_length, d_plot_width);
home_area = area(d_home_side, d_home_side);
time_taken = time(plot_area, home_area, d_mow_rate);
cout << "It will take " << time_taken << " minutes to mow this lawn. Better get cracking" << endl;
return 0;
}
double area(double length, double width) {
double value;
value = length * width;
return value;
}
double time(double p_area, double h_area, double mow_rate) {
double value;
value = (p_area - h_area) / mow_rate;
return value;
}
I am struggling to understand how the time() function works.
So far I understand that :
time_taken , gets its value from the time() function: time(plot_area, home_area, d_mow_rate).
The time() function gets its values from the function declaration at the bottom.
double time(double p_area, double h_area, double mow_rate) {
double value;
value = (p_area - h_area) / mow_rate;
return value;
}
However, this is where I'm stuck. The user is asked to enter values for d_plot_length, d_plot_width, etc. So I cannot understand how the compiler knows what these values p_area, and h_area actually are.
I realise that somehow the area() function is being used to aid the time() function, but as far as I'm aware the variables P_area etc within the time() function do not have values assigned to them.
Please can someone fill in the gaps in my understanding.
To be more precise, I want to know exactly how time_taken is displayed on the screen, from the start of the process, to the cout. Like I say I am familiar with most areas but not all.
In your program, you had computed the following values:
plot_area = area(d_plot_length, d_plot_width);
home_area = area(d_home_side, d_home_side);
When the method area(double,double) is invoked, the resultant double value gets stored in these variables.
Then you have the function call:
time_taken = time(plot_area, home_area, d_mow_rate);
This is the call by value type of function invocation. A copy of the values in the variables, plot_area, home_area and d_mow_rate are passed to the function. In the time(double, double, double) the computing is done upon the basis of the logic you had defined in this method and the resultant value is returned to the function call in the main() method.
Please note that the function call is of call by value and hence only a copy of the values are passed to the arguments mentioned in the function time(double, double, double) even though the variable names are the same in the main() and in the function call.
For further reading, I will suggest you to have a look at the following links:
Call By
Value
Call By
Reference
Call By
Pointer
I need to write need a function to compute power in C++
I don't understand why my code below is wrong.
ex. : base: 2 exponent 3 -> result: 4.48498e-306
if i use "int" the result is -> 2
#include <iostream>
#include <cstdlib>
#include <cmath>
using namespace std;
double power(double base, double exponent);
int main()
{
double base, exponent, power;
cout << "Enter a base " << endl;
cin >> base;
cout << "Enter an exponent" << endl;
cin >> exponent;
cout << "The result is ': "<< power << endl;
return 0;
}
double power(double base, double exponent)
{
int i;
double s=1;
for (i = 0; i < exponent; ++i)
s *= base;
return s;
}
What am I doing wrong?
In your code you have two declarations of power.
double power(double base, double esponente);
double base,esponente,power;
You declare the variable power but you never initialize it before printing it, so it's going to be undefined. Rerunning your program will actually give you a different number, in all likelihood. You need to remove this local variable declaration, as it shadows the global function declaration.
Then, instead of
cout<<"\nL'elevamento a potenza e': "<<power<<endl;
You want this line:
cout<<"\nL'elevamento a potenza e': "<<power(base, esponente)<<endl;
You are either printing the address of the function power or printing the uninitialized value of the double power the way you have written the code. (Technically you are hitting an uninitialized shadowed variable). In any case, you are not even calling the function you wrote... How does the power function know to be called? With what arguments?
Fix 1. Suggest you delete the 'double' of power.
Fix 2. Actually call the function and use/store/print the result
example.
After getting input from user do this:
double result = power( base, exponent );
cout << result << endl;
To print the result.
You need call function like this, with parameters:
Here is your main. You don't need local variable power. You want call function with name power.
int main ()
{
double base,esponente;
cout<<" \n Inserisci base \n";
cin>>base;
cout<<"\nInserisci esponente\n";
cin>>esponente;
cout<<"\nL'elevamento a potenza e': "<<power(base,esponente)<<endl;
system ("PAUSE");
}
I am writing code to call functions having to do with force, mass, and acceleration equations. The functions are called correctly, but the inputs are not multiplied as they should be. My output for the first function is a crazy small number, and the output for the first function is always 0.
Here is my code. Any feedback wold be very helpful. Thanks.
#include <iostream>
#include <cstdlib>
using namespace std;
void displayMenu();
double force(double);
double secondForce(double,double);
int main(int argc, char** argv)
{
int menuOption;
displayMenu();
system("PAUSE");
return 0;
}
void displayMenu(void)
{
int menuOption;
double weight, accel;
cout << " Main Menu" << endl;
cout << "Enter 1 for Force calculation with acceleration = 9.8m/s^2.\n";
cout << "Enter 2 for Force calculation with user defined acceleration.\n";
cout << "Enter 3 to quit the program.\n";
cin >> menuOption;
if(menuOption==1)
{
cout << "Enter a mass.\n";
cin >> weight;
cout << "The force is ";
cout << force(weight);
cout << "N.";
}
else if(menuOption==2){
cout << "Enter a mass.\n";
cin >> weight;
cout << "Enter an acceleration.\n";
cin >> accel;
cout << "The force is ";
cout << secondForce(weight, accel);
cout << "N.";
}
}
double force(double weight)
{
double force, mass;
force=(mass*(9.8));
return force;
}
double secondForce(double secondMass, double secondWeight)
{
double secondForce, mass, acceleration;
secondForce=(mass*acceleration);
return secondForce;
}
You are using uninitialized variables in your functions. Using these uninitialized variables in your program is undefined behavior.
force=(mass*(9.8)); << mass has a garbage value
secondForce=(mass*acceleration); << mass and acceleration have a garbage value
I think you meant to have
double force(double weight)
{
return weight * 9.8;
}
double secondForce(double secondMass, double secondAccel)
{
return secondMAss * secondAccel;
}
The problem is you are using variables in your calculation that are undefined. See my embedded comments below:
double secondForce(double secondMass, double secondWeight)
{
double secondForce, mass, acceleration;
secondForce=(mass*acceleration); //what is the value of mass and acceleration here??
return secondForce;
}
As a side note: Consider stepping through your code inside of a debugger like gdb so you can see how your program executes. Trying to reason through it is very difficult for large programs. In your example, it's easy to spot for an experienced programmer.
You're multiplying the data by garbage values
double force(double weight)
{
double force, mass;
force=(mass*(9.8));
return force;
}
double secondForce(double secondMass, double secondWeight)
{
double secondForce, mass, acceleration;
secondForce=(mass*acceleration);
return secondForce;
}
What's the value of mass and acceleration here? These variables are not initialized. You have to assign some values to them first.
You should enable compiler warnings and pay attention to them. For example, here is what MSVC says even on the lowest warning level:
warning C4700: uninitialized local variable 'mass' used
warning C4700: uninitialized local variable 'mass' used
warning C4700: uninitialized local variable 'acceleration' used
In C++, using an uninitialised variable is never a good idea. Unlike in other languages, most variables in C++ are not automatically initialised with 0 values. This causes your program to inhibit unspecified or undefined behaviour when the value contained in the variable is to be accessed.
Be safe and correct. Initialise! For example:
double force = 0.0;
double mass = 0.0;
Note that the language also allows you to first initialise, then assign, then use the variable. For example:
double force;
force = 0.0;
cout << force;
But that's bad style. Why leave a variable uninitialised and then later assign something when you can do everything in one step? Leaving the variable uninitialised first also prevents you from making it const.
Ensuring correct initialisation of all variables will make the behaviour of your program defined and consistent. You will have other problems, though, because you multiply the 0 mass, which will always result in 0 and is certainly not what you intend. However, deterministic behaviour is a good starting point to fix the wrong math.