Search vector by line number

[naegleria73]

I've been working on a program that stores the data from a fasta file to a vector. The user can then search the vector by searching for a line number and the program will output the header line and the sequence line that comes beneath the header line. My code is nowhere near finished so I apologize in advance for that. My question is, how would I be able to search by line number as opposed to line content. For example if I type "55", the program will output ">55" and then the sequence beneath it. Right now, I have to type in the whole header line to search for it.
Here's a portion of my input file (fasta file):
seq1
GGGCCCAU-A

>se2
CAUUAGAU-G

>seq3
GCGCCCGU-A

>seq4
GCGGAAGU-A

>5
GUGGACGU-G
>6
GCCGGGGU-G
>7
GGGGCCUU-A

>8
GGUCCGGU-A
>9
GCGGGUGU-A
>seq10
GGGCCUGU-A

  //Homework #5 - Fasta File Reader Program
//Anneliese Schorpp-Dettmann

#include <iostream>       //directives
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>
#include <stdio.h>
#include <cstdlib>


using namespace std;

int main (){                                                                            //main program begins
ifstream fastafile;                                                                     //variables
string  content, line, filename;
vector <string> myvector;
string name;
int seqLength=0;
vector <string>:: iterator it;

 cout<<"Input fasta file name: " << endl;                                               //prompt user to input a fasta file name
   getline(cin, filename);

  fastafile.open(filename.c_str ());                                                    //open fasta file
  while (!fastafile.is_open ()) {

	  cout <<"Fasta file could not be opened. Session terminated."<<endl;

	  exit (EXIT_FAILURE);                                                              //ends program if fasta file cannot be opened
	  break;
  }


  while(getline (fastafile, line)) {
	  
     seqLength= line.length();
	 
		 fastafile >> line;                                                             //store data from fasta file to vector
	                      
	myvector.push_back(line);
	
	cout <<line<<endl; 

  }
 
cout<<"Select sequence number."<<endl;                                                  //prompt user to enter a sequence number
getline (cin, name);
it = find (myvector.begin(), myvector.end (), name);
if (it != myvector.end()) {
	
	cout<<"The name of your molecule is:"<<endl;                                       
	cout<<*it<<endl;
}
else {
	cout <<"The name of the sequence number you entered could not be found."<<endl;
	exit (EXIT_FAILURE);                                                                
}



cout<<"The sequence of your molecule is:"<<endl;





cout<<"The length of your sequence is:"<<seqLength<<endl;


cout<<"There are a total of "<< myvector.size ()/2 <<" sequences in your alignment."<<endl;
 


   return 0; 
   }

[keskiverto]

What does the "line number" actually mean and what is the formal description of this "fasta" format?

[gunnerfunner]

OP: a std::map might be more appropriate in this case with 55, as in your example, stored as the key and the sequence beneath it as the value

[Handy Andy]

Hello naegleria73,

If you want to extract from the vector by using a number you could usemyvector[x] with 'x' being a subscript just as you would use with an array. Otherwise the search that you have will work.

Hope that helps,

Andy