Using a Variable as an Array Parameter in C++

Question

I am trying to write code that will compare a 10 sequence piece of DNA to that of a relative's 10 sequence DNA. The user inputs their name, how many relatives they want to compare, and their DNA. The computer outputs the percentage of a match. ATTAGACGCA compared to ATAAGACGCA would match 90%. The number of relatives is a constant after the user states how many relatives. I have tried using const, but it doesn't seem to want to use the number.

/**********************************************************************
 * Get DNA Sequence
 ***********************************************************************/
void getMyDNA(char myDNA[])
{
   cout << "Enter your DNA sequence: ";
   cin >> myDNA;
}

/**********************************************************************
 * Get Potential Relatives
 ***********************************************************************/
int getRelatives()
{
   int relatives = 0;
   cout << "Enter the number of potential relatives: ";
   cin >> relatives;

   return relatives;
}

/**********************************************************************
 * Get Potential Relatives Names
 ***********************************************************************/
void getRelativeName(string relativeNames[], int relatives)
{
   string name;
   for (int i = 0; i < relatives; i++)
   {
      cout << "Please enter the name of relative #" << i + 1 << ": ";
      cin >> name;
      relativeNames[i] = name;
   }
}

/**********************************************************************
 * Get Potential Relatives DNA Sequence
 ***********************************************************************/
void getRelativeDNA(char relativeDNA[][10], string relativeNames[], int relatives)
{
   for (int i = 0; i < relatives; i++)
   {
      cout << "Please enter the DNA sequence for " << relativeNames[i] << ": ";
      cin >> relativeDNA[i];
   }
}

/**********************************************************************
 * Display Potential Relatives Match
 ***********************************************************************/
void displayMatch(string relativeNames, char relativeDNA[][10], int relatives, char myDNA[])
{
   const int family = relatives;
   int count[family] = 0;
   for (int r = 0; r < 3; r++) //relative number r
   {
      for (int d = 0; d < 10; d++) //dna piece number d
      {
         if (relativeDNA[r][d] == myDNA[d])
            count[r]++;
      }
   }
}

/**********************************************************************
 * Main
 ***********************************************************************/
int main()
{
   char myDNA[10];
   string relativeNames[50];
   char relativeDNA[50][10];

   // My DNA
   getMyDNA(myDNA);


   //# of relatives
   int relatives = getRelatives();
   cout << endl;

   //thier names
   getRelativeName(relativeNames,relatives);
   cout << endl;


   //their dna
   getRelativeDNA(relativeDNA,relativeNames,relatives);
   cout << endl;

   //display
   displayMatch(relativeNames,relativeDNA,relatives,myDNA);

   return 0;
}

C++ doesn't have variable-length arrays so technically that's not valid C++. If you want a variable-length array use std::vector. — Some programmer dude
– Some programmer dude, Commented Apr 23, 2016 at 2:18
Also, what is count supposed to do? Is it an array or not? — Some programmer dude
– Some programmer dude, Commented Apr 23, 2016 at 2:20
I updated my question to include my entire code. Count is supposed to count how many letters in the sequence of DNA between me and my relative are the same. — Elise Riplie
– Elise Riplie, Commented Apr 25, 2016 at 19:22

Cheers and hth. - Alf · Accepted Answer · 2016-04-23 02:39:13Z

2

Instead of

int count[relatives] = 0;

which is invalid as standard C++ when relatives can vary at run-time, use

std::vector<int> count( relatives );

Include the <vector> header.

answered Apr 23, 2016 at 2:39

Cheers and hth. - Alf

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2 Comments

Matt C Over a year ago

Even if relatives couldn't vary, wouldn't it still be invalid code? You can't assign an entire array to an integer.

Cheers and hth. - Alf Over a year ago

@MatthewCliatt: Yes, the initializer would have to be fixed, like {0} (or just {}).

Harry · Accepted Answer · 2016-04-23 02:46:39Z

2

If count is a new array create a new array dynamically as follows...

int *count = new int[relatives];

I noticed you're using the following later...

count++;

Are you trying to increment an integer or move a pointer? This code might help make it clearer...

#include <assert.h>
#include <iostream>
#include <typeinfo>

int main(void) {
  const int x = 500;
  int* a = new int[x];
  size_t i = 0;
  for(i = 0; i < x;i++) {
    a[i] = i;
  }

  for(i = 0; i < x;i++) {
    //Print numbers without moving pointer
    std::cout << a[i] << std::endl;
  }
  for(i = 0; i < x;i++) {
    //Print numbers moving pointer
    std::cout << a[0] << std::endl;
    a++;
  }
  a = a - x;
  delete[] a;
  return 0;
}

edited Apr 23, 2016 at 2:46

answered Apr 23, 2016 at 2:26

Harry

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3 Comments

Cheers and hth. - Alf Over a year ago

Advising a beginner to use new for array is diabolic.

PaulMcKenzie Over a year ago

And no mention of using delete[ ].

Harry Over a year ago

I'll fix it up in a tick

Fabio Carballo · Accepted Answer · 2016-04-23 02:50:20Z

2

Even if the parameter is passed as const it won't work. You can try with an array created dynamically

int *count = new int[relatives];

edited Apr 23, 2016 at 2:50

answered Apr 23, 2016 at 2:31

Fabio Carballo

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2 Comments

PaulMcKenzie Over a year ago

Please do not use the term vector to describe what you're advising the OP.

Matt C Over a year ago

I'm not sure "dynamic array" is a good term for this. Its size is variable, but the array is in no way dynamic.

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