View Compilation Error

0_0_16897555_5926.cpp: In function 'Matrix mul(Matrix, Matrix, LL)':
0_0_16897555_5926.cpp:20:39: error: 'memset' was not declared in this scope
     memset(ret.mat, 0, sizeof(ret.mat));
                                       ^
0_0_16897555_5926.cpp: In function 'int main(int, const char**)':
0_0_16897555_5926.cpp:59:41: error: 'memset' was not declared in this scope
         memset(ans.mat,0,sizeof(ans.mat));
                                         ^