View Compilation Error

0_0_30117296_23765.cpp: In function 'mat mat_mul(mat, mat)':
0_0_30117296_23765.cpp:13:32: error: 'memset' was not declared in this scope
  memset(res.a, 0, sizeof(res.a));
                                ^
0_0_30117296_23765.cpp: In function 'void pow(int)':
0_0_30117296_23765.cpp:25:32: error: 'memset' was not declared in this scope
  memset(res.a, 0, sizeof(res.a));
                                ^