CODEWITHSUNDEEP
c++pointersmatrixmultiplication
Alan Watts
Alan Watts

Reputation: 33

Multiplication Matrix Code in C++ keeps crashing whenever I run it. Cannot figure out why

The code is supposed to add together 2 matrices and output a 3rd one tht is the result of the first two. I think this should work, but whenever I try to run it I get an error!

It looks like my post is mostly code but I think I explained enough.

    #include<iostream>

        using namespace std;

        //Study........
        int main()
        {
        int matrixC[10][10];
        int l,m,z,n;
    cout<< "Please input the dimensions of the first matrix"<< endl;//MatrixA
    cin>> l;
    cin>> m;
        int **matrixA = new int*[l];


        for(int i = 0; i < l; i++)
        {
    matrixA[i] = new int[m];
        }
        for(int i=0; i < l; i++){
    delete [] matrixA[i];
        }
    delete [] matrixA;

    cout<< "Please input the dimensions of the second matrix"<< endl;//MatrixA
    cin>> z;
    cin>> n;
int **matrixB = new int*[l];


for(int i = 0; i < l; i++)
{
    matrixB[i] = new int[m];
}
for(int i=0; i < l; i++){
    delete [] matrixB[i];
}
    delete [] matrixB;


/*cout<<"enter the dimension of the first matrix"<<endl;
cin>>l>>m;
cout<<"enter the dimension of the second matrix"<<endl;
cin>>z>>n;
if(m!=z||z!=m){
cout<<"error in the multiplication enter new dimensions"<<endl;
cout<<"enter the dimension of the first matrix"<<endl;
cin>>l>>m;
cout<<"enter the dimension of the second matrix"<<endl;
cin>>z>>n;
}*/


cout<<"enter the first matrix"<<endl;
for(int i=0;i<l;i++){
for(int j=0;j<m;j++){
     cin>>matrixA[i][j];
     }
     }
cout<<"enter the second matrix"<<endl;
for(int i=0;i<z;i++){
for(int j=0;j<n;j++){
    cin>>matrixB[i][j];
}
}
for(int i=0;i<l;i++){
for(int j=0;j<n;j++){
        matrixC[i][j]=0;
        for(int k=0;k<m;k++){
matrixC[i][j]=matrixC[i][j]+(matrixA[i][k] * matrixB[k][j]);
}
}


cout<<"your matrix is"<<endl;
for(int i=0;i<l;i++){
for(int j=0;j<n;j++){
cout<<matrixC[i][j]<<" ";
}
cout<<endl;
}
}
//system("pause");
return 0;
}

Upvotes: 0

Views: 147

Answers (2)

Nick Weedon
Nick Weedon

Reputation: 451

There are two problems:

a) You delete Matrix A & B after allocating

b) You never allocate Matrix C

Upvotes: 0

Vladimir Kolesnikov
Vladimir Kolesnikov

Reputation: 991

No wonder… You delete[] both matrixA and matrixB and then the code like cin>>matrixA[i][j] causes the crash because of invalid memory writes.

Upvotes: 5

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