I'm trying to implement boundary tests in CppUnit. I want to check the limit value itself as well as the boundaries around this limit.
For the upper boundary I wanted to add the smallest inkrement possible. For double this increment can be accessed with
numeric_limits<double>::epsilon()
However, if I add epsilon to my limit I get Not-a-Number (NaN) as result:
#include <stdio.h>
#include <iostream>
#include <limits>
#include <math.h>
using namespace std;
const double WARNING_LIMIT = 8000.0;
int main(void) {
double warningLowerLimit = WARNING_LIMIT - numeric_limits<double>::epsilon();
if(warningLowerLimit < WARNING_LIMIT ) {
cout << "lower" << endl;
}
else if (warningLowerLimit > WARNING_LIMIT) {
cout << "upper" << endl;
}
else if ( fabs(warningLowerLimit) < 0.001) {
cout << "same" << endl;
}
else {
cout << "NaN" << endl; // <-- result
}
}
Can somebody please explain me, why the result is not lower that the limit?
Best regards
else if ( fabs(warningLowerLimit) < 0.001) {
cout << "same" << endl;
}
That should be
fabs(warningLowerLimit - WARNING_LIMIT)
there. Without checking the difference, you get to the cout << "NaN" if warningLowerLimit == WARNING_LIMIT for example.
Related
What the program does is allows the user to input a bunch of strings, stores them in a stack, and then outputs all of those strings in the stack but in reverse order and flipped. Is there a more efficient way of doing what I did? Maybe using a different data structure (other than a stack)? I though a stack would be best because the strings stored in the stacks need to be outputted in the opposite order that they were inputted.
Here's the code:
#include <iostream>
#include <stack>
using namespace std;
int main() {
stack <string> elements;
string element;
cout << "Hello, welcome to Flippy-McBackwardson! \n\n" << endl;
cout << "Please enter a bunch of strings (type END to terminate your list): " << endl;
do {
getline(cin, element);
elements.push(element);
} while (element != "END");
elements.pop();
cout << "\nFlippy Backward Version: " << endl;
for (int x = elements.size()-1; x >= 0; x--){
for (int i = elements.top().length()-1; i >= 0; i--){
cout << elements.top()[i];
}
elements.pop();
cout << endl;
}
return 0;
}
You can use reverse iterators (accessible using std::rbegin() and std::rend()) which should be cleaner and safer as they don't involve tricky subscripting math that is prone to off-by-one errors (at the very least).
while(!elements.empty())
{
std::for_each(std::rbegin(elements.top()), std::rend(elements.top()),
[](char c){ std::cout << c; });
std::cout << '\n';
elements.pop();
}
What is the correct way to determine if a number (in my case it is a value of power of two calculated by pow(2,n)) is within the limits of values that one variable type can take? I'm doing it like this: if(pow (2,128)>std::numeric_limits<float>::max()), but this is evaluated as true although it is expected that float's maximum value is 2^128 or something more. Is there any better way to do this comparison?
For these kinds of limit checking, you can move the terms around to stay within the limits of the type.
In this case, pow(2,n) == exp(ln(2)*n) mathematically, so, rearranging terms, you can use n > ln(maxval)/ln(2)
You can take the base 2 logarithm of the maximum limit for the type of variable and compare it to n. For example: if(n > std::log2(std::numeric_limits<float>::max()). You probably don't want n to be exactly on the limit though, since I think stuff like floating point error might cause some problems.
First of all can you answer what is the result of pow(2, 128)?
The real question is what is the type for this expression?
The second question is do you know how floating point numbers work?
Take a look on this code to give you a hints:
#include <cmath>
#include <iostream>
#include <limits>
template<class T>
void printInfo(const std::string& desc, T x)
{
std::cout << desc << ' ' << typeid(x).name() << ' ' << x << std::endl;
}
int main()
{
printInfo("A", std::pow(2, 128));
printInfo("B", std::pow(2.0f, 128));
printInfo("A", std::pow(2, 128.0f));
auto c = std::pow(2.0f, 128.0f);
printInfo("C", c);
std::cout << (c > std::numeric_limits<float>::max()) << std::endl;
std::cout << (c == std::numeric_limits<float>::infinity()) << std::endl;
return 0;
}
https://wandbox.org/permlink/bHdKqToDKdC0hSvW
I recommend review documentation of numeric_limits.
And analyze this code:
#include <cmath>
#include <iostream>
#include <limits>
template<class T>
void print2exp()
{
std::cout << typeid(T).name() << '\n';
std::cout << "Radix = " << std::numeric_limits<T>::radix << '\n';
auto maxExp = std::numeric_limits<T>::max_exponent;
std::cout << "Max exp = " << maxExp << '\n';
std::cout << "2^maxExp = " << std::pow(static_cast<T>(2), static_cast<T>(maxExp)) << '\n';
std::cout << "2^(maxExp - 1) = " << std::pow(static_cast<T>(2), static_cast<T>(maxExp - 1)) << '\n';
}
int main()
{
print2exp<float>();
print2exp<double>();
print2exp<long double>();
return 0;
}
https://wandbox.org/permlink/J0hACKUKvKlV8lYK
So proper approach to this is (assuming that radix is 2):
if (x < std::numeric_limits<T>::max_exponent) {
return std::pow(static_cast<T>(2), static_cast<T>(x));
} else {
throw invalid_argument("x is to big to be use as 2^x");
}
I do not know how to declare "random" in the parentheses for "int main()," and need help. (I am a beginner in C++)
Please take a look at my code, try it out, and please notify me with an answer when you think you know how to solve this problem. It'd mean a lot to me. Thanks! Meanwhile, I will keep trying to solve the problem myself as well.
Note: I am using Code::Blocks if you want to be specific.
The error is on Line 7/9 of my code.
Here is my updated code below:
#include <iostream>
#include <stdlib.h>
#include <conio.h>
using namespace std;
int main()
{
int rn = random() % 21; // generates a random int from 0 to 20
// First output asking the user to guess the number
cout << "Please guess my number :" << endl;
int u;
cin >> u;
while (u != rn) // Calculates the answer that you give
{
// If the user's number is greater than the random number
// the program will let you know it's too large
if (u > rn)
{
cout << "You guessed too big!" << endl;
}
// On the other hand, if the user guesses to small
// the program will tell them that it's too small
else if (u < rn)
{
cout << "You guessed too small!" << endl;
}
// If the user does not get the right number, the program
// will tell the user to guess again
cout << "Please guess again :" << endl;
cin >> u;
}
// If the user guesses the number correctly, the program
// will say that they got it right, and end the program
cout << "You guessed it right!" << endl;
getch();
}
Here's the updated compiler error:
||=== Build: Debug in Guess The Number (compiler: GNU GCC Compiler) ===|
C:\Users\Minecraftship\Documents\CPP Programs From Book\Guess The Number\main.cpp||In function 'int main()':|
C:\Users\Minecraftship\Documents\CPP Programs From Book\Guess The Number\main.cpp|12|
error: 'randomize' was not declared in this scope|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|
Remove the semicolon near main, the compiler is telling you exactly what the issue is:
int main ();
Should be
int main ()
Your code will also not compile even after fixing this because you have not declared the std namespace. You can put this line at the top for now using namespace std; but it is bad practice. You should declare it manually using the scope resolution operator.
And a number of other issues as already mentioned in the comments above, make sure to read the compiler output thoroughly because it tells you what line is causing the issue.
Your code should look like:
#include <iostream>
#include <stdlib.h>
#include <conio.h>
using namespace std;
int main()
{
int rn = random() % 21; // generates a random int from 0 to 20
// First output asking the user to guess the number
cout << "Please guess my number :" << endl;
int u;
cin >> u;
while (u != rn) // Calculates the answer that you give
{
// If the user's number is greater than the random number
// the program will let you know it's too large
if (u > rn)
{
cout << "You guessed too big!" << endl;
}
// On the other hand, if the user guesses to small
// the program will tell them that it's too small
else if (u < rn)
{
cout << "You guessed too small!" << endl;
}
// If the user does not get the right number, the program
// will tell the user to guess again
cout << "Please guess again :" << endl;
cin >> u;
}
// If the user guesses the number correctly, the program
// will say that they got it right, and end the program
cout << "You guessed it right!" << endl;
getch();
}
Someone else got to it. There are no semicolons after signatures to methods like main().
One other thing not mentioned, I'm guessing you want
while (u != rn)
Also, be careful of the difference in "=" and "==".
BTW -- Welcome to C++!!!
a little more portable version (doesn't use conio.h) which lets the computer play against himself:
#include <iostream>
#include <cstdlib>
#include <ctime>
int get_random_in_range(int min, int max)
{
return std::rand() % (max - min) + min;
}
// returns 0 if user guessed right, negative value if user
// guessed too small, positive if user guessed too big
int check_user_guess(int guess, int my_secret)
{
return guess - my_secret;
}
int main ()
{
int my_guess = get_random_in_range(1, 10);
std::cout << "I think of " << my_guess << std::endl;
std::cout << "Please guess my number: ";
int user_guess = get_random_in_range(1, 10);
std::cout << user_guess << std::endl;
while (check_user_guess(user_guess, my_guess) != 0)
{
std::cout << "You guessed " << user_guess << std::endl;
if (check_user_guess(user_guess, my_guess) > 0)
{
std::cout << "You guessed too big!" << std::endl;
}
else if (check_user_guess(user_guess, my_guess) < 0)
{
std::cout << "You guessed too small!" << std::endl;
}
std::cout << "Please guess again: ";
user_guess = get_random_in_range(1, 10);
std::cout << user_guess << std::endl;
}
std::cout << std::endl << "You guessed it right!";
}
try it here: http://coliru.stacked-crooked.com/a/5bf0b9201ef57529
I've been assigned a project to determine the square root of a number without using division or the math.h library. Upon doing my own research I've decided to tackle the problem by using the bisection method. I used the pseudo code portion from the Bisection Wikipedia page:
https://en.wikipedia.org/wiki/Bisection_method#Example:_Finding_the_root_of_a_polynomial
to setup the algorithm.
My Code
#include <iostream>
#include <cmath>
#include <stdlib.h>
using namespace std;
void __attribute__((weak)) check(double alt_sqrt(double));
//default check function - definition may be changed - will not be graded
void __attribute__((weak)) check(double alt_sqrt(double))
{
if(alt_sqrt(123456789.0) == sqrt(123456789.0))cout << "PASS\n";
else cout << "FAIL\n";
return;
}
//change this definition - will be graded by a different check function
double my_sqrt(double x)
{
int i = 0;
double a = 0.0; // Lower Bound
double b = x + 1; // Upper Bound
double c = 0.0; // Guess for square root
double error = 0.00001;
double fc = 0.0;
while(i < 10000)
{
c = (a+b)*0.5;
fc = c * c - x;
if(abs(fc) < error || (b-a)*0.5 < error) // Check for solution
{
cout << "Square root is: " << c << endl;
break;
}
if(fc < 0) // Setup new interval
{
a = c;
cout << "a is: " << a << endl;
}
else b = c;
cout << "b is: " << b << endl;
i++;
}
return c;
}
//Do not change this function
int main()
{
check(my_sqrt);
return 0;
}
The output I am currently getting for my professor's test case in main is
Square root is: 1.23457e+08
FAIL
When the correct output should be
Square root is: 11,111.11106
PASS
I believe that I am going wrong in the way that I setup my new intervals. My thinking is that if the difference between the two values is negative, then I need to push the lower bound up, and if the difference is positive, then I need to bump the upper bound down.
I would appreciate any advice y'all could give me. Thank you for your time.
The condition fb - fa < 0 is wrong because ignoring floating-point errors, fa < fb, which is a * a - x < b * b < x will be always true for 0 <= a < b.
Changing the condition to fc < 0 improved the accuracy, but unfortunately this improvement coundl't make the program print "PASS". To improve the accuracy to have the program print "PASS", delete the harmful breaking part
if(abs(fc) < error || (b-a)*0.5 < error) // Check for solution
{
cout << "Square root is: " << c << endl;
break;
}
Removing this harmful breaking and adding the line
cout << "Square root is: " << c << endl;
just before
return c;
gave me
Square root is: 11111.1
PASS
but unfortunately this is not what you want.
To have what you want printed,
#include <iomanip>
should be added and the printing part should be
std::cout.imbue(std::locale(""));
cout << fixed << setprecision(5) << "Square root is: " << c << endl;
I'm having a little trouble with my code. It's pretty much supposed to open two files, and compare the first twenty line of the file "StudentAnswers.txt" [inputted as a char into a char array] against a char value in (each line of another file) "CorrectAnswers.txt" in another array at the same position (index). It's like a linear search, but the same position in the arrays. Then a report should be displayed, detailing which question the student missed, the given answer, the correct answer, and if the student passed (got >= 70%) or not, like the following:
Report for Student X:
2 (A/D), 3 (C/D), 5(D/A)
This student passed the exam!
Then it should clear the SAArray, and feed the next twenty lines from StudentAnswers.txt, and start the process all over again. I guess the program has to determine the number of students from (lines of 'StudentAnswers.txt' file / 20).
I'm having trouble displaying the report, and having the array clear itself after the program. I'm guessing this can be done with a while loop and an accumulator for the number of students (to be determined by above equation).
Also, Visual Studio seems to go to "Missed __ questions for a total of ___ %", and then keep looping -858993460.
Any help would be appreciated.
#include <iostream>
#include <fstream>
#include <string>
#include <array>
#include <algorithm>
using namespace std;
void GradeReturn(char[], char[], int, int, int);
string PassFail(float);
int main()
{
ifstream SA("StudentAnswers.txt");
ifstream CA("CorrectAnswers.txt");char CAArray[20];
char SAArray[20];
// char SA2Array[20];
bool isCorrect;
int correct;
int incorrect;
int counter;
correct = 0;incorrect = 0;
counter = 0;
cout << endl;
if (!SA.fail())
{
cout << "'StudentAnswers.txt' file opened successfully." << endl;
cout << "'CorrectAnswers.txt' file opened successfully." << endl << endl;
int a = 0;
int b = 0;
while (a < 20)
{
CA >> CAArray[a];
a++;
} // while loop to feed char into the array
while (b < 20)
{
SA >> SAArray[b];
b++;
}
} // while loop to feed char into array
CA.close(); // closing "CorrectAnswers.txt"
SA.close(); // closing "StudentAnswers.txt"
GradeReturn(&CAArray[counter], &SAArray[counter], correct, incorrect, counter);
return 0;
}
void GradeReturn(char CAArray[], char SAArray[], int correct, int incorrect, int counter)
{
float percent;
float hundred;
int student;
int catcher[20];
int writeCatcher; int starter;
int catcher_size;
student = 0;
writeCatcher = 0;
catcher_size = ((sizeof catcher) / 4);
while (counter < 20)
{
if ((CAArray[counter]) == (SAArray[counter]))
{
correct++;
cout << "Good job!" << endl;
} // correct handling
else
{
incorrect++;
cout << "You got question " << counter << " wrong." << endl;
counter >> catcher[writeCatcher];
writeCatcher++;
} // incorrect handling
counter++;
} // while loop to determine if a student got a question right or wrong
static_cast <float> (incorrect); // float conversion
cout << endl; // for cleanliness
percent = ((static_cast <float> (correct)) / 20); // percentage
hundred = percent * 100;
PassFail(percent);
if (PassFail(percent) == "pass")
{
student++;
cout << "Report for Student " << student << ":" << endl;
cout << "-----------------------------" << endl;
cout << "Missed " << incorrect << " questions out of 20 for ";
cout << hundred << " % correct." << endl << endl;
starter = 0;
while (starter < (sizeof catcher)
{
if(1=1)
{
catcher_size
}
else
{
cout << "";
starter++;
}
}
}
else if (PassFail(percent) == "fail")
{
student++;
cout << "Missed " << incorrect << " questions out of 20 for ";
cout << hundred << " % correct." << endl << endl;
while (starter < catcher_size)
{
if ((catcher[starter]) == -858993460)
{
starter++;
}
else
{
cout << "";
starter++;
}
}
}
return;
}
string PassFail(float percent)
{
if (percent >= 0.70) // if <pass>
{
return "pass";
}
else // if <fail>
{
return "fail";
}
cout << endl;
}
To get a loop you should keep streams open instead of closing them after reading 20 lines.
As pseudo code that would be:
a = 0;
while(streams_not_empty)
{
CA >> CAArray[a];
SA >> SAArray[a];
++a;
if (a == 20)
{
GradeReturn(&CAArray[counter], &SAArray[counter], correct, incorrect, counter);
a = 0; // Reset a
}
}
CA.close(); // closing "CorrectAnswers.txt"
SA.close(); // closing "StudentAnswers.txt"
You would also need to pass correct, incorrect, counter by reference so that the GradeReturn can change their value and their by do the accumulation.
Like:
void GradeReturn(char CAArray[], char SAArray[], int& correct, int& incorrect, int& counter)
Further you shouldn't rely on being able to read exactly Nx20 lines from the files every time. A file could have, e.g. 108 (5x20 + 8) lines, so you code should be able to handle the with only 8 lines. In other words, don't hard code 20 in your function like while (counter < 20). Instead pass the number of lines to be handled and do while (counter < number_to_handle).
Something like this as pseudo code:
a = 0;
while(streams_not_empty)
{
CA >> CAArray[a];
SA >> SAArray[a];
++a;
if (a == 20)
{
GradeReturn(&CAArray[counter], &SAArray[counter], correct, incorrect, counter, a);
// ^
a = 0; // Reset a
}
}
if (a != 0)
{
// Process the rest
GradeReturn(&CAArray[counter], &SAArray[counter], correct, incorrect, counter, a);
}
CA.close(); // closing "CorrectAnswers.txt"
SA.close(); // closing "StudentAnswers.txt"
One problem you have is you're trying to compare C-style strings with the == operator. This will compare them essentially as if they were pointers to char, i.e. compare whether they point at the same location in memory, not compare the contents of the string. I urge you to look up array-decay and c-string variables to understand more.
Specifically, if (PassFail(percent) == "pass") isn't going to do what you want it to. strcomp doc, strncmp doc using std::string variables instead of c-style strings would all work, but it would be better simply to compare percent to a value, i.e. if(percent >= 0.70 directly instead of calling PassFail and comparing a string.
There are many other issues here also, you at one point call PassFail but do nothing with the return value. The only side affect of PassFail is cout << endl, if that's what you intend, it's a poor decision and hard to read way to put a newline on the console.
Try asking your compiler for more warnings, that's often helpful in finding these types of issues. -Wall -Wextra work for gcc, you may have to read your compiler manual...