View Compilation Error

0_0_15052112_23094.cpp: In function 'bool Gauss()':
0_0_15052112_23094.cpp:42:20: error: 'fabs' was not declared in this scope
    if (fabs(a[i][c])>fabs(a[max_r][c]))
                    ^
0_0_15052112_23094.cpp:46:23: error: 'fabs' was not declared in this scope
   if (fabs(a[max_r][c]) < eps) return 0;
                       ^
0_0_15052112_23094.cpp: In function 'int main()':
0_0_15052112_23094.cpp:95:27: error: 'memset' was not declared in this scope
   memset(du, 0, sizeof(du));
                           ^