foo.cpp: In constructor 'matrix::matrix()':
foo.cpp:12:35: error: 'memset' was not declared in this scope
     matrix(){ memset(a,0,sizeof(a)); }
                                   ^
foo.cpp: In function 'void dfs(int)':
foo.cpp:48:32: error: 'memset' was not declared in this scope
         memset(f,0xff,sizeof(f));
                                ^
foo.cpp: In function 'void dfs2(int, int*, int)':
foo.cpp:78:32: error: 'memset' was not declared in this scope
         memset(f,0xff,sizeof(f));
                                ^
foo.cpp: In function 'void build_matrix()':
foo.cpp:118:33: error: 'memset' was not declared in this scope
         memset(use,0,sizeof(use));
                                 ^
foo.cpp: In function 'int matrix_pow()':
foo.cpp:138:11: warning: unused variable 'j' [-Wunused-variable]
     int i,j;
           ^
foo.cpp: In function 'int main()':
foo.cpp:161:29: error: 'memset' was not declared in this scope
     memset(use,0,sizeof(use));
                             ^