View Compilation Error

0_0_13809911_10935.cpp: In function 'int cmp(const void*, const void*)':
0_0_13809911_10935.cpp:18:27: error: 'strcmp' was not declared in this scope
     if(!strcmp(c->b1,d->b1))
                           ^
0_0_13809911_10935.cpp:36:30: error: 'strcmp' was not declared in this scope
     return strcmp(c->b1,d->b1);
                              ^
0_0_13809911_10935.cpp: In function 'int main()':
0_0_13809911_10935.cpp:67:46: error: 'strcmp' was not declared in this scope
             while(!strcmp(in[i].b1,in[i+1].b1)&&i<n-1)
                                              ^