Finding Length Of The Longest String

#include<iostream>
using namespace std;
int lon(char a[][30],int);
int main()
{
    char a[10][30];
    int m,i;
    cout<<"Enter num of strings:";
    cin>>m;
    cout<<"\nEnter the strings:\n\n";
    for(i=0;i<=m;++i)
    {
        cin.getline(a[i],30);
    }
    cout<<"The result is: "<<lon(a,m);
    return 0;

}
int lon(char a[][30],int m)
{
    int max,i;
    max=strlen(a[0]);
    for(i=0;i<=m;++i)
    {
        if(max<strlen(a[i]))
        max=strlen(a[i]);
    }
    return max;
}