This is my code for finding the sum of a harmonic series of 1/n. I want it to stop when the sum is greater than or equal to 15, but the code cannot run. Can anyone let me know what I'm doing wrong? It seems to follow the correct while loop structure. Thanks!
#include <iostream>
using namespace std;
int main ()
{
int divisor = 1;
int sum = 1;
while ((sum <= 15) && (divisor >=1))
{
sum = sum + (1/divisor);
divisor++;
}
cout << "You need " << divisor << " terms to get a sum <= 15" << endl;
return 0;
}
Your loop is actually running. However, your sum variable is of type int, and so is divisor.
1 (an int) / divisor (also an int) will return 1 or 0. This is because you are doing integer division. 1/1 == 1. However, 1/2 == 0, 1/3 == 0, etc... To solve this, cast divisor to double:
(1 / (double)divisor)
So that solves the issue of that segment returning only 1 or 0. However, you will still gain a sum of 1 as sum is of type int. Attempting to assign a double to an int variable will result in a truncation, or floor rounding. Sum will add the first 1, but it will remain 1 indefinitely after that. In order to solve this, change the type of sum to double.
Your assignment of sum = 1; is a logical error. Your result will be 1 higher than it should be. Your output statement is also mistaken... It should be...
cout << "You need " << divisor << " terms to get a sum > 15" << endl;
In addition, the condition of divisor >= 1 is needless... It is always greater than or equal to one because you assign it as 1 and are incrementing... If you do want a sum that is >= 15, change the while condition to...
while (sum < 15)
Your code should look like this...
#include <iostream>
using namespace std;
int main()
{
int divisor = 1;
double sum = 0; //Changed the type to double and assigned 0 rather than 1
while (sum <= 15) //While condition shortened...
{
sum = sum + (1 / (double)divisor); //Added type cast to divisor
divisor++;
}
//cout statement adjusted...
cout << "You need " << divisor << " terms to get a sum > 15" << endl;
return 0;
}
Related
I am new to coding and my task is to make the variable 'sum' greater than (not equal to) m by summing up 1/n for an increasing 'n'.
I need to solve the same problem twice (one using a for-loop and once using a while-loop). But both ways end in an infinte loop.
My code is working fine when I replace the "<=" with "<". But that
Can someone help me?
#include <iostream>
using namespace std;
int main () {
unsigned int m = 1;
double sum = 0;
long n;
n = 1;
while (sum <= m) //THIS LINE
{
double sumsum = 1/n;
sum += sumsum;
n++;
}
cout << "n = " << n << endl ;
cout << "sum = " << sum << endl ;
return 0;
}
Epression 1/n with n being of type long and having a value > 1 will always yield 0, since you operate with integral types. Hence, sum will be assigned 1 in the first run, but will never come to a value > 1, as forth on always 0 is added.
Change your code to
double sumsum = 1.0/n;
and it should work. Note that 1.0 enforces to operate with floating points.
I understand I can just use for-loop to define prime number, but before I implement for loop into that topic, I had a thought that I maybe could make one with while loop or do-while.
Somehow, my do-while loop seems not to be working correctly.
My theory was that I could find prime number for checking the remainder of divisor where divisor keeps decreasing by 1 until divisor reaches 1. (Although 'until divisor reaches 1.' part is not in the code, I would assumed remainder of 0 would appear anyway before divisor goes below 0.)
However, it keeps halting before remainder reaches 0.
What did I do wrong?
I've even tried both instead of (remainder<1 && remainder!=1)below but still no luck.
while (remainder<1)
while (remainder==1)
#include <iostream>
using namespace std;
int main()
{
int number, divisor, remainder;
cin >> number;
divisor=number-1;
cout << "You've put " << number << ".\n";
do {
divisor = divisor - 1;
remainder=number%divisor;
}
while (remainder<1 && remainder!=1);
cout << divisor << " " << remainder << " " << number << " " << "Divisor, remainder, number\n";
return 0;
}
First, you have a typo in your variable assignment. This line:
number = divisor - 1;
should be:
divisor = number - 1;
The while() condition should be while (remainder != 0), so that the loop keeps repeating as long as you haven't found a divisor. If you want to be more explicit, you could use while (divisor > 1 && remainder != 0). There's no need to repeat when divisor == 1 because that's a divisor of all integers.
I'm having a problem with the following simple code, I don't know why the output will become negative... The program is supposed to calculate the sum of all odd and five-digit numbers like 10001, 10003, 10005, etc.
#include <iostream>
using namespace std;
int main()
{
int num, sum = 0;
for (num = 10001 ; num <= 99999 ; num+=2){
sum += num;
}
cout << num << " " << sum;
return 0;
}
It means that there is an overflow of type int. That is this type can not represent the sum. I advice to declare variable sum like
long long int sum = 0;
After that you can compare the result with the maximum value stored in type int. For example
#include <limits>
//...
std::cout << std::numeric_limits<int>::max() << " " << sum << std::endl;;
Your int will likely overflow. Switch it to long
int num = 0;
long long sum = 0L;
Assuming you have a 4 byte int, the maximum value will be 2^31 - 1 == 2147483647. See this example
Your sum will come out to 2475000000 which will overflow.
Im having trouble with the function taylor2 not returning a value if i input anything over 2. If I enter 0-2 it outputs the correct value but anything over 2 and I just get a flashing underscore with no data returned.
void taylor2(double x)
{
double total = 1;
int i = 0;
int count = 1;
double temp = 1;
do
{
{
if (i % 2 == 1)
{
temp = (pow(x, i * 2 + 2) / factorial(i * 2 + 2));
total += temp;
}
else {
temp = (pow(x, i * 2 + 2) / factorial(i * 2 + 2));
total -= temp;
}
}
count++;
i++;
} while (fabs(temp) >= .0001);
cout << "The last recoreded temporary value was: "<<temp << endl;
cout << "The computed value for cosine is : "<< total << endl;
cout << "It took " <<count << " values to calculate the value of the function to .0001 places"<< endl;
cout << endl;
}
I suspect that factorial is returning an int. If int is 32 bit (very common), then factorial will overflow once the argument reaches 13 (i = 5 in your case). Signed integer overflow is undefined behaviour in C++.
You could use a std::uint64_t (an unsigned 64 bit integer). This will allow you to evaluate a few larger factorials.
For more reference, see Calculating large factorials in C++
Better still, use a recurrence relation between your Taylor terms.
I am currently writing a program that estimates Pi values using three different formulas pictured here: http://i.imgur.com/LkSdzXm.png .
This is my program so far:
#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;
int main()
{
double leibniz = 0.0; // pi value calculated from Leibniz
double counter = 0.0; // starting value
double eulerall = 0.0; // pi value calculated from Euler (all integers)
double eulerodd = 0.0; // value calculated from Euler (odds)
int terms;
bool negatives = false;
cin >> terms;
cout << fixed << setprecision(12); // set digits after decimal to 12 \
while(terms > counter){
leibniz = 4*(pow(-1, counter)) / (2*counter+1) + leibniz;
counter++;
eulerall = sqrt(6/pow(counter+1,2)) + eulerall;
counter++;
eulerodd = (sqrt(32)*pow(-1, counter)) / (2*counter + 1) + eulerodd;
counter++;
cout << terms << " " << leibniz << " " << eulerall << " " << eulerodd <<endl;
}
if (terms < 0){
if(!negatives)
negatives=true;
cout << "There were " << negatives << " negative values read" << endl;
}
return 0;
}
The sample input file that I am using is:
1
6
-5
100
-1000000
0
And the sample output for this input file is:
1 4.000000000000 2.449489742783 3.174802103936
6 2.976046176046 2.991376494748 3.141291949057
100 3.131592903559 3.132076531809 3.141592586052
When I run my program all I get as an output is:
1 4.000000000000 1.224744871392 1.131370849898.
So as you can see my first problem is that the second and third of my equations are wrong and I can't figure out why. My second problem is that the program only reads the first input value and stops there. I was hoping you guys could help me figure this out. Help is greatly appreciated.
You have three problems:
First, you do not implement the Euler formulae correctly.
π2/6 = 1/12 + 1/22 + 1/32 + ...
eulerall = sqrt(6/pow(counter+1,2)) + eulerall;
The square root of the sum is not the sum of the square roots.
π3/32 = 1/13 + 1/33 + 1/53 + ...
eulerodd = (sqrt(32)*pow(-1, counter)) / (2*counter + 1) + eulerodd;
This is just... wrong.
Second, you increment counter three times in the loop, instead of once:
while(terms > counter){
...
counter++;
...
counter++;
...
counter++;
...
}
Third, and most fundamental, you didn't follow the basic rule of software development: start small and simple, add complexity as little at a time, test at every step, and never add to code that doesn't work.
my first problem is that the second and third of my equations are
wrong and I can't figure out why
Use counter++ just once. Apart from this Leibniz looks fine.
Eulerall is not correct, you should sum all factors and then do sqrt and multiplication at the end:
eulerall = 1/pow(counter+1,2) + eulerall;
// do sqrt and multiplication at the end to get Pi
The similar thing with eulerodd: you should sum all factors and then do sqrt and multiplication at the end.
My second problem is that the program only reads the first input value
and stops there.
In fact this is your first problem. This is because you are incrementing counter multiple times:
while(terms > counter){
leibniz = 4*(pow(-1, counter)) / (2*counter+1) + leibniz;
counter++; // << increment
^^^^^^^^^^
eulerall = sqrt(6/pow(counter+1,2)) + eulerall;
counter++; // << increment
^^^^^^^^^^
eulerodd = (sqrt(32)*pow(-1, counter)) / (2*counter + 1) + eulerodd;
counter++; // << increment
^^^^^^^^^^
cout << terms << " " << leibniz << " " << eulerall << " " << eulerodd <<endl;
}
You should increment counter just once.
You're using the same counter and incrementing it after each calculation. So each technique is only accounting for every third term. You should increment counter only once, at the end of the loop.
Also note that it is generally bad form to use a floating-point value as a loop counter. It only takes on integer values in your program, so you can just make it an int. Nothing else needs to change; the math will run the same because the int will promote to a double when you combine the two in math operations.
#include<iostream>
#include<conio.h>
#include<cmath>
using namespace std;
char* main()
{
while(1)
{
int Precision;
float answer = 0;
cout<<"Enter your desired precision to find pi number : ";
cin>>Precision;
for(int i = 1;i <= Precision;++i)
{
int sign = (pow((-1),static_cast<float>(i + 1)));
answer += sign * 4 * ( 1 / float( 2 * i - 1));
}
cout<<"Your answer is equal to : "<<answer<<endl;
_getch();
_flushall();
system("cls");
}
return "That is f...";
}