View Compilation Error

0_0_22065825_17377.cpp: In function 'mat mat_mul(mat, mat)':
0_0_22065825_17377.cpp:17:30: error: 'memset' was not declared in this scope
  memset(res.a, 0, sizeof(res));
                              ^
0_0_22065825_17377.cpp: In function 'll mat_pow(ll)':
0_0_22065825_17377.cpp:30:30: error: 'memset' was not declared in this scope
  memset(res.a, 0, sizeof(res));
                              ^