View Compilation Error

0_0_20623121_5695.cpp: In constructor 'BigNum::BigNum()':
0_0_20623121_5695.cpp:17:24: error: 'memset' was not declared in this scope
    memset(a,0,sizeof(a));}
                        ^
0_0_20623121_5695.cpp: In constructor 'BigNum::BigNum(int)':
0_0_20623121_5695.cpp:40:24: error: 'memset' was not declared in this scope
    memset(a,0,sizeof(a));
                        ^
0_0_20623121_5695.cpp: In copy constructor 'BigNum::BigNum(const BigNum&)':
0_0_20623121_5695.cpp:51:24: error: 'memset' was not declared in this scope
    memset(a,0,sizeof(a));
                        ^
0_0_20623121_5695.cpp: In member function 'BigNum& BigNum::operator=(const BigNum&)':
0_0_20623121_5695.cpp:70:24: error: 'memset' was not declared in this scope
    memset(a,0,sizeof(a));
                        ^