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Finding the highest value inside a vector

DDomjosa (89)
Hi, so I have a vector with a few double values and I need to find the highest of them. When I run this, the console freezes:

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double highest(std::vector<double>& A)
{
    double highest = A[0];
    for (unsigned int i=1;i<A.size();i++)
        if (A[i] > highest)
            highest = A[i];
    return highest;
}


If I do the same with normal arrays, it works just fine (n is the size of the array):

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double highest(double A[], int n)
{
    double highest = A[0];
    for (int i=1;i<n;i++)
        if (A[i] > highest)
            highest = A[i];
    return highest;
}


Where did I go wrong while doing it with a vector?
closed account (E0p9LyTq)
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#include <iostream>
#include <vector>

double highest(std::vector<double>);

int main()
{
   std::vector<double> A = { 52.5, 9.2, 4.7, 97.3, 8.1 };

   double largest = highest(A);

   std::cout << "The highest is " << largest << std::endl;
   
   return 0;
}

double highest(std::vector<double> A)
{
   double highest = A[0];
   for (unsigned int i = 1; i < A.size(); i++)
   {
      if (A[i] > highest)
      {
         highest = A[i];
      }
   }
   return highest;
}


Notice carefully the function declaration/definition. No & reference needed.
Last edited on
DDomjosa (89)
The reference is so that the whole vector isn't copied each time and doesn't take up as much memory. Your code works just as well with a reference.

Also your code is exactly the same as my code, I think there's a problem with how I write the values from a .txt file to the vector instead:

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void read(std::vector<double>& A)
{
    std::ifstream fd(Cfd);
    for (unsigned int i=0;i<A.size();i++)
        fd >> A[i];
}


Is this a valid way of writing from a file to a vector? Works well with arrays...

EDIT:

The .txt file would contain values separated by spaces such as:
 
 
4.99 6 7 42.1 964.99 0.99
Last edited on
DDomjosa (89)
Absolutely nothing I can think of works:

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void read(std::vector<double>& A)
{
    std::ifstream fd(Cfd);
    for (unsigned int i=0;i<A.size();i++)
    {
        double x;
        fd >> x;
        A[i] = x;
    }
}


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void read(std::vector<double>& A)
{
    std::ifstream fd(Cfd);
    for (unsigned int i=0;i<A.size();i++)
    {
        double x;
        fd >> x;
        A.push_back(x);
    }
}


Can someone please tell me what am I doing wrong?..
Kevin C (319)
Your code in function highest seems fine.

Post the entire working program. Please cut out all the unnecessary parts.
DDomjosa (89)
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#include <iostream>
#include <fstream>
#include <iomanip>
#include <vector>
const char Cfd[] = "Data.txt", Cfr[] = "Results.txt";
void read(std::vector<double>&), print(const std::vector<double>&, double), descending(std::vector<double>&);
double highest(std::vector<double>&);
int main()
{
    std::vector<double> A;
    read(A);
    descending(A);
    print(A, highest(A));
    return 0;
}
void read(std::vector<double>& A)
{
    std::ifstream fd(Cfd);
    for (unsigned int i=0;i<A.size();i++)
        fd >> A[i];
}
double highest(std::vector<double>& A)
{
    double highest = A[0];
    for (unsigned int i=1;i<A.size();i++)
        if (A[i] > highest)
            highest = A[i];
    return highest;
}
void descending(std::vector<double>& A)
{
    for (unsigned int i=0;i<A.size();i++)
    {
        for (unsigned int j=i+1;j<A.size();j++)
            if (A[i] < A[j])
            {
                double t = A[i];
                A[i] = A[j];
                A[j] = t;
            }
    }
}
void print(const std::vector<double>& A, double x)
{
    std::ofstream fr(Cfr);
    fr << "Highest value is " << std::fixed << std::setprecision(2) << x << std::endl;
    for (unsigned int i=0;i<A.size();i++)
        fr << A[i] << " ";
}


In theory, if the Data.txt contains values 4.99 6 7 42.1 964.99 0.99, the Results.txt should contain 
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Highest value is 964.99
964.99 42.10 7.00 6.00 4.99 0.99
Kevin C (319)
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void read(std::vector<double>& A)
{
    std::ifstream fd(Cfd);
    for (unsigned int i=0;i<A.size();i++)


The size of A is zero here.

Either define A to have 6 elements, or rewrite your read function to read until end of file.
Last edited on
DDomjosa (89)
How can I make the function read until the end of file? Could you give an example please?

EDIT:

Also, if I use 6 instead of A.size(), it still freezes the console...

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void read(std::vector<double>& A)
{
    std::ifstream fd(Cfd);
    for (unsigned int i=0;i<6;i++)
        fd >> A[i];
}
Last edited on
Kevin C (319)
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int main()
{
    std::vector<double> A(6);



The aboove is unnecessary if you read until EOF:

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double input;
while(fd>>input)
    A.push_back(input);
Last edited on
DDomjosa (89)
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void read(std::vector<double>& A)
{
    std::ifstream fd(Cfd);
    double input;
    while(fd>>input)
        A.push_back(input);
}


Still the console freezes...

If I put the read function like it is above AND I add the (6) to the vector, it doesn't freeze, but the ouput file is 
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Highest value is 0.00
0.00 0.00 0.00 0.00 0.00 0.00


EDIT:

It wasn't reading the file properly for some odd reason, I deleted the old one and created a new one from scratch and now it works perfectly even without the (6). Thank you for the help!
Last edited on
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