View Compilation Error

0_0_20751476_21396.cpp: In function 'bool cmp1(people, people)':
0_0_20751476_21396.cpp:12:25: error: 'strcmp' was not declared in this scope
  return strcmp(a.ID,b.ID)<0;
                         ^
0_0_20751476_21396.cpp: In function 'bool cmp2(people, people)':
0_0_20751476_21396.cpp:16:25: error: 'strcmp' was not declared in this scope
  if(strcmp(a.name,b.name)!=0)
                         ^
0_0_20751476_21396.cpp: In function 'bool cmp3(people, people)':
0_0_20751476_21396.cpp:25:26: error: 'strcmp' was not declared in this scope
   return strcmp(a.ID,b.ID)<0;
                          ^