View Compilation Error

0_0_37104593_675.cpp: In function 'mop op(mop, mop)':
0_0_37104593_675.cpp:11:32: error: 'memset' was not declared in this scope
  memset(res.a, 0, sizeof(res.a));
                                ^
0_0_37104593_675.cpp: In function 'void lL(int)':
0_0_37104593_675.cpp:20:41: error: 'memset' was not declared in this scope
  mop res,c; memset(res.a,0,sizeof(res.a)); memset(c.a,0,sizeof(c.a)); c.a[1][1]=2;c.a[2][1]=1;c.a[3][1]=1;
                                         ^