View Compilation Error

0_0_16891121_1370.cpp: In function 'void mul(LL (*)[3], LL (*)[3])':
0_0_16891121_1370.cpp:32:24: error: 'memset' was not declared in this scope
  memset(c, 0, sizeof(c));
                        ^
0_0_16891121_1370.cpp: In function 'int main()':
0_0_16891121_1370.cpp:57:25: error: 'memset' was not declared in this scope
   memset(b, 0, sizeof(b));
                         ^