View Compilation Error

0_0_21005253_31004.cpp: In function 'mat operator*(mat, mat)':
0_0_21005253_31004.cpp:12:32: error: 'memset' was not declared in this scope
  memset(ans.a, 0, sizeof(ans.a));
                                ^
0_0_21005253_31004.cpp: In function 'mat qpow(mat, long long int)':
0_0_21005253_31004.cpp:25:32: error: 'memset' was not declared in this scope
  memset(ans.a, 0, sizeof(ans.a));
                                ^