Here is my code for printing the divisors and then number of divisors of a given number.
Now suppose I take 2 test cases: 5 and 8; this code gives count of 5 as 2 and 8 as 6 (i.e it adds the previous count).
Even if I declare it as int count = 0; it returns the same output.
The other problem arises when I declare int count = 0 inside function factors.
The code gives count as 0 for all cases.
#include<iostream>
using namespace std;
int count;
long long factors(long n, long f=1)
{
if(n%f==0) {
cout << f << endl;
count++;
}
if(f==n) {
return 0;
}
factors(n,f+1);
return count;
}
int main()
{
int n;
int t;
cin >> t;
while(t--)
{
cin >> n;
cout << factors(n) << endl;
}
return 0;
}
Using globals is not usually a good idea. It is especially bad in recursive functions, which should preferably be re-entrant. Of course you can fix your function by resetting the count in the loop, like this:
while(t--)
{
cin>>n;
count = 0; // Reset count before the recursive call
cout << factors(n) << endl;
}
You could also make factors "wrapper" that resets the count to free the callers from the need to reset count before calling factors, like this:
long long factors(long n) {
count = 0;
return factors(n, 1);
}
long long factors(long n,long f /* Remove the default */) {
... // the rest of your code
}
you can achieve this by passing count as reference -
#include<iostream>
using namespace std;
long long factors(long n, int& count, long f=1)
{
if(n%f==0)
{
cout<<f<<endl;
count = count + 1;
}
if(f==n)
return 0;
factors(n, count, f+1);
return 0;
}
int main()
{
int n,t;
cin>>t;
while(t--)
{
cin>>n;
int count = 0;
factors(n, count);
cout << count << endl;
}
return 0;
}
-Gaurav
First, why are you declaring the count variable in the global space?
Second, you can not perform arithmetic operations to an undeclared variable (the int "count" in this case is never declared).
Third, why do you create an infinite loop by doing while(t--)?
You said the function gives you count as 0 for all input,
Can this be due to count never being declared?
Related
I am trying to use pointers whenever possible in the following code and am having difficulty figuring out how, exactly, to institute the pointers and how to return a pointer value at the end of my first function. I have done some research on the subject but none of the methods I found have been helpful so far, so I was hoping you may have some specialized tips.
Note: I am a beginner.
#include <iostream>
using namespace std;
int mode(int *pies[], int size) {
int count = 1;
int max = 0;
int *mode=pies[0];
for (int i=0; i<size-1; i++)
{
if (pies[i] == pies[i+1])
{
count++;
if (count>max)
{
max = count;
mode = pies[i];
}
}
else
count = 1;
}
return *mode;
}
int main() {
int n;
cout<<"Input the number of people: "<<endl;
cin>>n;
int survey[n];
cout << "Enter the amount of pie eaten by each person:" << endl;
for(int i = 0; i < n; i++) {
cout <<"Person "<<(i + 1)<< ": "<<endl;
cin>>survey[i];
}
cout<<"Mode: "<<mode(survey, n)<< endl;
return 0;
}
Here is an attempt to answer.
In your main(), you call the mode() function with mode(survey, n) while int survey[n]; is an array of int, so you may use int mode(int *pies, int size) instead of int mode(int *pies[], int size) (as the array int survey[n] can be implicitly converted into pointer).
However, you need to modify two more things in your function:
int *mode=pies[0]; is wrong as pies[0] is the first element of an array of int, thus is an int, while int* mode is a pointer on an int which is incompatible. mode should be an int to receive pies[0]. The correct code is then int mode = pies[0].
Your function signature is int mode(int *pies, int size), thus, again, you should return an int. You should then just return mode;
These are only hints on how to make the code compile.
Your next step is to formalize what you would like it to do and then modify the code accordingly
NB: The correct practice is to think about what you would like to achieve first and then code afterwards (but let us say that this is for the sake of helping each other)
To get started using pointers, you may look at some simple tutorials at first:
http://www.cplusplus.com/doc/tutorial/arrays/
https://www.programiz.com/c-programming/c-pointers
https://www.programiz.com/c-programming/c-pointers-arrays
https://www.geeksforgeeks.org/pointer-array-array-pointer/
https://www.geeksforgeeks.org/how-to-return-a-pointer-from-a-function-in-c/
https://www.tutorialspoint.com/cprogramming/c_return_pointer_from_functions.htm
Here is the modified code with the stated modifications above (it compiles):
#include <iostream>
using namespace std;
int mode(int *pies, int size) {
int count = 1;
int max = 0;
int mode=pies[0];
for (int i=0; i<size-1; i++)
{
if (pies[i] == pies[i+1])
{
count++;
if (count>max)
{
max = count;
mode = pies[i];
}
}
else
count = 1;
}
return mode;
}
int main() {
int n;
cout<<"Input the number of people: "<<endl;
cin>>n;
int survey[n];
cout << "Enter the amount of pie eaten by each person:" << endl;
for(int i = 0; i < n; i++) {
cout <<"Person "<<(i + 1)<< ": "<<endl;
cin>>survey[i];
}
cout<<"Mode: "<<mode(survey, n)<< endl;
return 0;
}
This is the program for printing out sum of array elements. It is showing run time error. The output is coming out to be 0 instead of printing out the sum of the elements.
#include<iostream.h>
using namespace std;
void simpleArraySum()
{
int ar[100],n,i,sum=0;
for(i=0;i<n;i++)
{
sum=sum + ar[i];
}
cout<<sum;
}
int main()
{
int ar[100],n;
cin>>n;
for(int i=0;i<n;i++)
{
cin>>ar[i];
}
simpleArraySum();
return 0;
}
On this line in your main:
int ar[100], n;
You create an array of 100 elements. You later fill that array using cin
for(int i = 0 ; i < n ; i++)
{
cin >> ar[i];
}
Then you do nothing with that array. You are not calculating any sum. You let that array go, forgotten.
Then, you call a simpleArraySum function. That function is creating an entirely new, distinct array.
// v-----v------There
int ar[100],n,i,sum=0;
That array has no value assigned to it. In fact, reading from it is undefined behavior.
What you want is to receive that array in the arguments of your function:
void simpleArraySum(int* ar, int n) {
// ...
}
And call it like that in your main:
simpleArraySum(ar, 100);
You can avoid the issues of arrays and functions by not using them:
int main()
{
int quantity = 0;
std::cin >> quantity;
int sum = 0;
int value;
while (std::cin >> value)
{
sum += value;
}
std::cout << sum << "\n";
return EXIT_SUCCESS;
}
In simpleArraySum, the variable n is uninitialized. So this loop:
for(i=0;i<n;i++)
invokes undefined behavior when reading from n.
Also, you are summing a different array in the function, than the one you read in mian. It seems that you need to pass in the array from main to this function:
void simpleArraySum(int *ar, int n) {
and call it like this:
simpleArraySum(ar, n);
Finally, you don't even need a function for this, since there is an existing algorithm std::accumulate that you can use:
cout << std::accumulate(ar, ar + n, 0);
In the function, you're adding the elements of ar which is local to the function simpleArraySum() and is not of the array ar that is local to main().
So, pass the array and its length to the function and return its sum. Here is your corrected code:
#include<iostream>
using namespace std;
void simpleArraySum(int ar[], int n)
{
int i, sum = 0;
for(i=0;i<n;i++)
{
sum=sum + ar[i];
}
cout<<sum;
}
int main()
{
int ar[100],n;
cin>>n;
for(int i=0;i<n;i++)
{
cin>>ar[i];
}
simpleArraySum(ar, n);
return 0;
}
I'm testing a recursive function that returns the number of occurrence of a given number in an array. I get an unexpected result when I run the code.
#include <iostream.h>
int Occurence(int A[], int size, int n)
{
static int occur=0;
if(size == 0)
{
int occur2 = (int) occur;
return occur2;
}
else
{
if ( n == A[size-1])
occur++;
Occurence(A, size-1, n);
}
}
int main()
{
int A[] = {1,3,2,5,1,2, 3, 7,7, 8,8, 4, 6, 9,9, 0};
int size = sizeof(A)/sizeof(A[0]);
int n;
cout<< "Enter Number to Find : ";
cin >>n;
cout<<endl;
cout<<"Number of Occurence of "<< n << " is :"<< Occurence(A, size, n)<<endl;
return 0;
}
You are missing a return at the end of your function. If size is not 0 then the behaviour of your function is undefined. Adding the return should make it work:
int Occurence(int A[], int size, int n)
{
static int occur=0;
if(size == 0)
{
int occur2 = (int) occur;
return occur2;
}
else
{
if ( n == A[size-1])
occur++;
return Occurence(A, size-1, n);
}
}
Recursion is a very strange way to implement this problem so I assume this is some toy example to demonstrate how recursion works. Even if this is the case you really shouldn't be using a static variable in your implementation. Just make each call return the current sum instead:
int Occurence(int A[], int size, int n)
{
if(size == 0)
{
return 0;
}
else
{
return (n == A[size-1] ? 1 : 0) + Occurence(A, size-1, n);
}
}
This version will return the correct result when called multiple times whereas your original would add to the previous count each time.
In real code simply do:
#include <algorithm>
int Occurence(int A[], int size, int n)
{
return std::count(A, A+size, n);
}
There are some compilation problems in your code. First of all, in C++, the standard library files usually don't have an extension in the filename. So, including <iostream.h> is wrong. You should include <iostream>.
Other problem with your code is that you are using cout and cin without specifying their namespaces. So, instead of using cout and cin directly, use std::cout and std::cin or declare use namespace std after your includes.
EDIT: as Thomas Matthews pointed out, prefer using std::cout and std::cin over using namespace std.
I am writing a simple code to calculate Fabonacci numbers as an exercise. The code works, but i don't get why. I have some special cases for n=1 and n=2 which is the place of the number in the sequence (the numbers are 0 and 1). However after those, the number is calculated in this loop.
while(n>LoopCount)
{
Fib_n=Fib_1+Fib_2;
Fib_2=Fib_1;
Fib_1=Fib_n;
LoopCount++;
}
Going in to the loop, Fib_1=0, Fib_2=0, and Fib_n=1. Why does not this loop just spit out 0 no matter what? The whole code is below.
#include <iostream>
using namespace std;
int main()
{
cout <<"Which number of the Fibonacci sequence do you want to calculate?" <<endl;
int n;
cin >>n;
cout <<endl;
int Fib_n;
int Fib_1;
int Fib_2;
int LoopCount=1;
if(n>1)
{
Fib_n=1;
LoopCount++;
while(n>LoopCount)
{
Fib_n=Fib_1+Fib_2;
Fib_2=Fib_1;
Fib_1=Fib_n;
LoopCount++;
}
}
cout <<Fib_n;
return 0;
}
int Fib_1;
int Fib_2;
were never initialized. Therefore, the first time you calculate Fib_n=Fib_1+Fib_2;, Fib_n will get the sum of two uninitialized variables.
I have modified your code so it would work.
#include <iostream>
using namespace std;
int main()
{
cout <<"Which number of the Fibonacci sequence do you want to calculate?" <<endl;
int n;
cin >> n;
cout << endl;
int Fib_1 = 1;
int Fib_2 = 1;
int count = 0;
while(n > count)
{
Fib_1 = Fib_1 + Fib_2;
Fib_2 = Fib_1 - Fib_2;
count++;
}
cout << Fib_1;
return 0;
}
Fib_1
You have that as an uninitalized variable, so you may get a garbage value for output.
Fib_2 = Fib_1
Next, you initialize Fib_2 with Fib_1, meaning they both share the same (random) value.
In debug mode, these are both initialized to 0, and adding them:
Fib_n=Fib_1+Fib_2;
makes the sum equal 0. In release mode, you can expect random values from the compiler. Here is more info on Uninitialized Variables.
I am considering a society where there are an arbitrary number of people. Each person has just two choices. Either he or she stays with her current choice or she switches. In the code that I want to write, the probability that the person switches is inputted by the user.
To make clear what I am trying to do, suppose that the user tells the computer that there are 3 people in the society where the probabilities that each person chooses to switch is given by (p1,p2,p3). Consider person 1. He has probability of p1 of switching. Using him as a base for our calculation, the probability given person 1 as a base, that exactly no one in the society chooses to switch is given by
P_{1}(0)=(1-p2)*(1-p3)
and the probability using person 1 as a base, that exactly one person in the society chooses to switch is given by
P_{1}(1)=p2*(1-p3)+(1-p2)*p3.
I can't figure out how to write this probability function in C++ without writing out every term in the sum. I considered using the binomial coefficient but I can't figure out a closed form expression for the sum since depending on user input, there are arbitrarily many probabilities that need to be considered.
I have attached what I have. The probability function is only a part of what I am trying to do but it is also the hardest part. I named the probability function probab and what I have in the for loop within the function is obviously wrong.
EDIT: Basically I want to calculate the probability of choosing a subset where each element in that subset has a different probability of being chosen.
I would appreciate any tips on how to go about this. Note that I am a beginner at C++ so any tips on improving my programming skills is also appreciated.
#include <iostream>
#include <vector>
using namespace std;
unsigned int factorial(unsigned int n);
unsigned int binomial(unsigned int bin, unsigned int cho);
double probab(int numOfPeople, vector<double> probs, int p, int num);
int main() {
char correctness;
int numOfPeople = 0;
cout << "Enter the # of people: ";
cin >> numOfPeople;
vector<double> probs(numOfPeople); // Create a vector of size numOfPeople;
for (int i = 1; i < numOfPeople+1; i++) {
cout << "Enter the probability of person "<< i << " will accept change: ";
cin >> probs[i-1];
}
cout << "You have entered the following probabilities of accepting change: (";
for (int i = 1; i < numOfPeople+1; i++) {
cout << probs[i-1];
if (i == numOfPeople) {
cout << ")";
}
else {
cout << ",";
}
}
cout << endl;
cout << "Is this correct? (Enter y for yes, n for no): ";
cin >> correctness;
if (correctness == 'n') {
return 0;
}
return 0;
}
unsigned int factorial(unsigned int n){ // Factorial function
unsigned int ret = 1;
for(unsigned int i = 1; i <= n; ++i) {
ret *= i;
}
return ret;
}
unsigned int binomial(unsigned int totl, unsigned int choose) { // Binomial function
unsigned int bin = 0;
bin = factorial(totl)/(factorial(choose)*factorial(totl-choose));
return bin;
}
double probab(int numOfPeople, vector<double> probs, int p, int num) { // Probability function
double prob = 0;
for (int i = 1; i < numOfPeople; i++) {
prob += binomial(numOfPeople, i-1)/probs[p]*probs[i-1];
}
return prob;
}
For future reference, for anybody attempting to do this, the probability function will look something like:
double probability (vector<double> &yesprobabilities, unsigned int numOfPeople, unsigned int yesNumber, unsigned int startIndex) {
double kprobability = 0;
// Not enough people!
if (numOfPeople-1 < yesNumber) {
kprobability = 0;
}
// n == k, the only way k people will say yes is if all the remaining people say yes.
else if (numOfPeople-1 == yesNumber) {
kprobability = 1;
for (int i = startIndex; i < numOfPeople-1; ++i) {
kprobability = kprobability * yesprobabilities[i];
}
}
else if (yesprobabilities[startIndex] == 1) {
kprobability += probability(yesprobabilities,numOfPeople-1,yesNumber-1,startIndex+1);
}
else {
// The first person says yes, k - 1 of the other persons have to say yes.
kprobability += yesprobabilities[startIndex] * probability(yesprobabilities,numOfPeople-1,yesNumber-1,startIndex+1);
// The first person says no, k of the other persons have to say yes.
kprobability += (1 - yesprobabilities[startIndex]) * probability(yesprobabilities,numOfPeople-1,yesNumber,startIndex+1);
}
return probability;
}
Something called a recursive function is used here. This is completely new to me and very illuminating. I credit this to Calle from Math stack exchange. I modified his version slightly to take vectors instead of arrays with some help.