Column Sum Of A Matrix

#include<iostream>
using namespace std;
void colsum(int [][30],int [],int,int);
int main()
{
    int a[30][30],b[30],m,n,i,j;
    cout<<"Enter row size: ";
    cin>>m;
    cout<<"Enter column size: ";
    cin>>n;
    cout<<"\n\nEnter the matrix: \n\n";
    for(i=0;i<m;++i)
    {
        for(j=0;j<n;++j)
        cin>>a[i][j];
    }
    cout<<"\n\nThe matrix is: \n\n";
    for(i=0;i<m;++i)
    {
        for(j=0;j<n;++j)
        {
            cout<<a[i][j]<<" ";
        }
        cout<<endl;
    }
    cout<<"\n\nThe column sum of the matrix is: \n\n";
    colsum(a,b,m,n);
    for(i=0;i<n;++i)
    cout<<b[i]<<" ";
    return 0;
}
void colsum(int a[][30],int b[],int m,int n)
{
    int i,j;
    b[n];
    for(j=0;j<n;++j)
    {
        b[j]=0;
        for(i=0;i<m;++i)
        {
            b[j]+=a[i][j];
        }
    }
}