与 char 比较的二维数组

Question

I have an array that reads data from a file, the data is binary digits such as 010011001001 and many others so the data are strings which I read in to my 2d array but I am stuck on comparing each value of the array to 0. Any help would be appreciated.

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    string myArr[5000][12];
    int i = 0, zeroCount = 0, oneCount = 0;
    
    ifstream inFile;
    inFile.open("Day3.txt");
    
    while(!inFile.eof())
    {
        for(int i = 0; i < 5000; i++)
        {
            for(int j = 0; j < 12; j++)
            {
                inFile >> myArr[i][j];
                j++;
            }
            i++;
        }   
    }
    
    for(int j = 0; j < 12; j++)
    {
        for(int i = 0; i < 5000; i++)
        {
            if(myArr[i][j].compare("0") == 0)
            {
                zeroCount++;
            }
            else
            {
                oneCount++;
            }
            i++;
        }
        
        if(zeroCount > oneCount)
        {
            cout << "Gamma is zero for column " << i << endl;
        }
        else
        {
            cout << "Gamma is One for column " << i << endl;
        }       
        j++;
    }
}

some input from the text file: 010110011101 101100111000 100100000011 111000010001 001100010011 010000111100

Answer 1

Thank you for editing you question and providing more information. Now, we can help you. You have 2 major misunderstandings.

1. How does a for loop work?
2. What is a std::string in C++

---

Let us start with the for loop. You find an explanation in the CPP reference here . Or, you could look also at the tutorial shown here .

The for loop has basically 3 parts: for (part1; part2; part3) . All are optional, you can use them, but no need to use them.

• part1 is the init-statement. Here you can declare/define/initialize a variable. In your case it is int i = 0 . You define a variable of data type int and initialize it with a value of 0
• part2 is the condition. The loop will run, until the condition becomes false. The condition will be check at the beginning of the loop.
• part3 is the so called iteration-expression. The term is a little bit misguiding. It is basically a statement that is executed at the end of the loop, before the next loop run will be executed and before the condition is checked again.

In Pseudo code it is something like this:

{

    init-statement
    while ( condition ) {

        statement
        iteration-expression ;

    } 
} 

which means for the part of your code for(int j = 0; j < 12; j++)

{

    int j = 0;                 // init-statement
    while ( j < 12 ) {         // while ( condition ) {

       inFile >> myArr[i][j];  // Your loop statements
       j++;                    // Your loop statements  PROBLEM

       j++;                    // iteration-expression from the for loop
    } 
} 

And now you see the problem. You unfortunately increment 'j' twice. You do not need to do that. The last part3 of the for loop does this for you already.

So please delete the duplicated increment statements.

---

Next, the std::string

A string is, as its names says, a string of characters, or in the context of programming languages, an array of characters.

In C we used to write actually char[42] = "abc"; . So using really a array of characters. The problem was always the fixed length of such a string. Here for example 42. In such an array you could store only 41 characters. If the string would be longer, then it could not work.

The inventors of C++ solved this problem. They created a dynamic character array, an array that can grow, if needed. They called this thing std::string . It does not have a predefined length. It will grow as needed.

Therefore, writing string myArr[5000][12]; shows that you did not fully understand this concept. You do not need [12] , becuase the string can hold the 12 characters already. So, you can delete it. They characters will implicitely be there. And if you write inFile >> myString then the extractor operator >> will read characters from the stream until the next space and then store it in your myString variable, regardless how long the string is.

Please read this tutorial about strings.

That is a big advantage over the C-Style strings.

Then your code could look like:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    string myArr[5000];
    int zeroCount = 0, oneCount = 0;

    ifstream inFile;
    inFile.open("Day3.txt");

    while (!inFile.eof())
    {
        for (int i = 0; i < 5000; i++)
        {
            inFile >> myArr[i];
        }
    }

    for (int i = 0; i < 5000; i++)
    {
        zeroCount = 0; oneCount = 0;
        for (int j = 0; j < 12; j++) 
        {

            if (myArr[i][j]== '0')
            {
                zeroCount++;
            }
            else
            {
                oneCount++;
            }
        }

        if (zeroCount > oneCount)
        {
            cout << "Gamma is zero for column " << i << endl;
        }
        else
        {
            cout << "Gamma is One for column " << i << endl;
        }
    }
}

But there is more. You use the magic number 5000 for your array of strings. This you do, because you think that 5000 is always big enough to hold all strings. But what, if not? If you have more than 5000 strings in your source file, then your code will crash.

Similar to the string problem for character arrays, we have also a array for any kind of data in C++, that can dynamically grow as needed. It is called std::vector and you can read about it here . A tutorial can be found here .

With that you can get rid of any C-Style array at all. But please continue to study the language C++ further and you will understand more and more.

Ther are more subtle problems in your code like while(.inFile.eof()) , but this should be solved later.

I hope I could help