View Compilation Error

0_0_31560008_10668.cpp: In function 'int long_mul(int*, int*, int*, int, int)':
0_0_31560008_10668.cpp:23:38: error: 'memset' was not declared in this scope
     memset(c, 0, (la+lb)*sizeof(c[0]));
                                      ^
0_0_31560008_10668.cpp: In function 'int long_add(int*, int*, int*, int, int)':
0_0_31560008_10668.cpp:41:46: error: 'memset' was not declared in this scope
     memset(c, 0, (max(la, lb)+1)*sizeof(c[0]));
                                              ^