View Compilation Error

0_0_15607403_28102.cpp: In constructor 'BigNum::BigNum()':
0_0_15607403_28102.cpp:15:40: error: 'memset' was not declared in this scope
     BigNum(){len=1;memset(a,0,sizeof(a));}
                                        ^
0_0_15607403_28102.cpp: In constructor 'BigNum::BigNum(int)':
0_0_15607403_28102.cpp:36:25: error: 'memset' was not declared in this scope
     memset(a,0,sizeof(a));
                         ^
0_0_15607403_28102.cpp: In function 'int main()':
0_0_15607403_28102.cpp:73:25: error: 'memset' was not declared in this scope
   memset(dp,0,sizeof(dp));
                         ^