请问我的哪里错了，结果运行不出来

#include
using namespace std;
int main()
{
int i, j, m, n;
int max, min, max_m, max_n, min_n, min_m;
int a[3][4] = { 1,2,3,4,5,6,7,8,9,10,11,12 };
cin >> a[0][0];
max = min = a[0][0];
max_m = min_m = 0;
max_n = min_n = 0;
for (i = 0; i < 3; i++)
for (j = 0; j < 4; j++)
{
cin >> a[i][j];
if (max < a[i][j])
{
max = a[i][j];
max_m = i;
max_n = j;
}
if (min > a[i][j])
{
min = a[i][j];
min_m = i;
min_n = j;
}
}
cout << max << endl;
cout << min << endl;
return 0;
std::cout << "Hello World!\n";
}

cin a[0][0]后下面有cin了一遍，要多输入一个a[0][0]

#include
using namespace std;
int main()
{
int i, j, m, n;
int max, min, max_m, max_n, min_n, min_m;
int a[3][4] = { 1,2,3,4,5,6,7,8,9,10,11,12 };
cin >> a[0][0];
max = min = a[0][0];
max_m = min_m = 0;
max_n = min_n = 0;
for (i = 0; i < 3; i++)
for (j = 0; j < 4; j++)
{
if(i!=0&&j!=0)
cin >> a[i][j];
if (max < a[i][j])
{
max = a[i][j];
max_m = i;
max_n = j;
}
if (min > a[i][j])
{
min = a[i][j];
min_m = i;
min_n = j;
}
}
cout << max << endl;
cout << min << endl;
return 0;
std::cout << "Hello World!\n";
}