View Compilation Error

0_0_33157125_14728.cpp: In function 'int cmp1(const void*, const void*)':
0_0_33157125_14728.cpp:13:48: error: 'strcmp' was not declared in this scope
   return strcmp((*(node*)a).num,(*(node*)b).num); 
                                                ^
0_0_33157125_14728.cpp: In function 'int cmp2(const void*, const void*)':
0_0_33157125_14728.cpp:17:45: error: 'strcmp' was not declared in this scope
  if(strcmp((*(node*)a).name,(*(node*)b).name)==0 )
                                             ^
0_0_33157125_14728.cpp: In function 'int cmp3(const void*, const void*)':
0_0_33157125_14728.cpp:25:48: error: 'strcmp' was not declared in this scope
   return strcmp((*(node*)a).num,(*(node*)b).num); 
                                                ^