Summing 2D array columns in c++ [closed] - c++

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I want to sum up columns of a predefined 2 D array, but my code seems not to work. E. g. for a 2D array with rows 2 3 and 4 5
I am getting following column sums:
-117393687 and -113194156
Here is the part of my code where I sum up the columns:
//sum columns
for(i=0; i<m; i++)
{
for(ii=0; ii<m; ii++)
{
sum += myarray[i][ii];
}
cout <<"column sum: "<<sum<<endl;
{
Rest of my code:
#include <iostream>
using namespace std;
int main()
{
int i, ii, n, m, sum;
int array[n][m];
sum=0;
cout <"no. of rows"<<endl;
cin>>n;
cout <"no. of columns"<<endl;
cin>>m;
for(i=0; i<n; i++)
{
for(ii=0; ii<n; ii++)
{
cout<<"row "<<i+1<<" column "<<ii+1<<endl;
cin>>array[n][m];
}
}
}
//sum columns
for(i=0; i<m; i++)
{
for(ii=0; ii<m; ii++)
{
sum += myarray[i][ii];
}
cout <<"column sum: "<<sum<<endl;
{

Answer 1

There are quite a few errors on your code, and it has quite a weird structure, but trying not to change it too much (so it's still easy for you to follow the fixes), let's see it fixed then I'll explain it (please note that this version will compile and run in practice):
#include <iostream>
using namespace std;
int main()
{
int i, ii, n, m, sum;
cout << "no. of rows" << endl;
cin >> n;
cout << "no. of columns" << endl;
cin >> m;
int array[n][m];
for (i=0; i<n; i++)
{
for (ii=0; ii<m; ii++)
{
cout << "row " << i+1 << " column " << ii+1 << endl;
cin >> array[i][ii];
}
}
sum=0;
for (i=0; i<n; i++)
{
for (ii=0; ii<m; ii++)
{
sum += array[i][ii];
}
}
cout << "Sum: " << sum << endl;
}
Ok, so, first, you should only declare the array after you know what "n" and "m" variables are. Edit: also, not all compilers will accept declaring the dynamic array that way, but again, I tried to keep your original structure as much as possible.
Second, in your input loop, you should index the array by "i" and "ii", but you were always indexing by "n" and "m", that is, only writing to the latest index, which would even cause an exception.
Last, while summing, again you should use "i" and "ii" as array indices, so you correctly scan the array.
And that is it.

Answer 2

You're not declaring your array size properly. When you create the array n and m aren't set yet. You need to determine their size first. And even then you have to pass in constants to an array because arrays in C++ cannot be dynamically sized. If you want the user to determine container size like this then use a vector of vectors. Arrays are to be used when you know the size from the beginning of the program.

Answer 3

According to the code shown above:
You are mistaking while taking the iputs. Try this:
for(i=0; i<n; i++)
{
for(ii=0; ii<n; ii++)
{
cout<<"row "<<i+1<<" column "<<ii+1<<endl;
cin>>array[i][ii];
}
}

Answer 4

You are initializing the 2D array in a wrong way, you need to define the size first, m and n are not initalized when declaring the array.
On C++ using containers like vector is better.
You also had a error in the input code (2 n instead of n and m in the for loop).
#include <iostream>
#include <vector>
using namespace std;
int main()
{
int rows, cols, sum = 0;
std::vector<std::vector<int>> array;
cout << "No. of rows: ";
cin >> rows;
cout << "No. of columns: ";
cin >> cols;
for(int i = 0; i< rows; i++)
{
std::vector<int> v;
for(int j = 0; j < cols; j++)
{
cout << "Value for row " << i + 1 << " and column "<< j + 1 << ": ";
int val;
cin >> val;
v.push_back(val);
}
array.push_back(v);
}
for (auto i: array)
{
for(auto j: i)
{
sum += j;
}
}
cout << "The sum is: " << sum << endl;
}