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Muhammed bakijev February 2016
### How do i output sum of rows of a 2D array C++

EDIT: I'm fairly new to c++. Began working with this language two weeks ago.

Sorry if this have been asked before, but i have searched everywhere on the web on how to sum individual rows in a 2D array and not found the answer that i was looking for.

i need to display the sum of each individual row in a[m][n], but for some reason this only works when my array is 2x2, but if it's 3x3 or bigger, then i get the following output in the terminal:

```
for intsance, a[3][3]=
{1,2,3}, //this is determined by the user
{1,2,3},
{1,2,3};
then i get the following output:
9179942 //address of some sort???
6 // actual sum. code is working here (yay :D)
469090925// again something i dont understand
```

This is what i have so far

```
#include <iostream>
using namespace std;
int main(){
int m,n;
cout<<"Enter number of rows for array"<<endl;
cin>>m;
if (m>10){
cout<<"More than 10 rows will be too big"<<endl;
return 1;
}
cout<<"Enter number of collumns for array"<<endl;
cin>>n;
if (n>10){
cout<<"More than 10 collumns will be too big"<<endl;
return 1;
}
int a[m][n];
for(int i=0; i<m;i++){
cout<<"Enter "<<m<<" values into row "<<i+1<<endl;
for(int j=0; j<n; j++){
cout<<"a ["<<i<<"]["<<j<<"]: ";
cin>>a[i][j];
}
}
cout<<"Array dimensions: "<<m<<"x"<<n<<'\n'<<"resulting array: "<<endl;
for(int i=0; i<m;i++){
for(int j=0; j<n; j++){
cout<<a[i][j]<<" ";
}
cout<<endl;
}
int avg[m];
int el_less_avg;
for(int i=0; i<m; i++){
for(int j=0; j<n;j++){
avg[i]+=a[i][j];
}
}cout<<"\n\n";
for(int i=0; i<m; i++){
cout<<avg[i]<<endl;
}
return 0;
}
```

kfsone February 2016

```
int avg[m];
int el_less_avg;
for(int i=0; i<m; i++){
for(int j=0; j<n;j++){
```

You're not initializing these values so they're free to be whatever cruft is on the stack at the time. You need to initialize them.

```
int avg[m];
for (int i = 0; i < m; ++i) {
avg[i] = 0;
for (int j = 0; j < n; ++j) {
avg[i] += a[i][j];
}
}
```

M.M February 2016

`int a[m][n];`

is not allowed in Standard C++. The dimensions of C-style arrays must be known at compile-time. A program using this code could do literally anything.

You could replace this line with:

```
vector<vector<int>> a(m, vector<int>(n));
```

which seems like a mouthful at first, but you will find it makes your problem go away.

Another bonus of this approach is that you can then use range-based loops:

```
for(int x : avg)
cout << x << endl;
```

which reduces the chance of making an error by using the wrong letter in the loop condition.

Asked in February 2016

Viewed 1,940 times

Voted 6

Answered 2 times

Viewed 1,940 times

Voted 6

Answered 2 times