View Compilation Error

0_0_24696093_8039.cpp:20:33: error: 'M' was not declared in this scope
 int n, m, t, len, a[3], x[2][3][M];
                                 ^
0_0_24696093_8039.cpp: In function 'int main()':
0_0_24696093_8039.cpp:33:25: error: 'x' was not declared in this scope
                         x[i][j][len] = t;
                         ^
0_0_24696093_8039.cpp:42:36: error: 'x' was not declared in this scope
                         if (a[j] < x[0][j][i] || a[j] > x[1][j][i]) fl = 0;
                                    ^