View Compilation Error

0_0_29356797_18307.cpp: In function 'int cmp1(node, node)':
0_0_29356797_18307.cpp:14:30: error: 'strcmp' was not declared in this scope
     return strcmp(a.num,b.num)<0;
                              ^
0_0_29356797_18307.cpp: In function 'int cmp2(node, node)':
0_0_29356797_18307.cpp:18:26: error: 'strcmp' was not declared in this scope
     if(strcmp(a.num,b.num)!=0)
                          ^
0_0_29356797_18307.cpp: In function 'int cmp3(node, node)':
0_0_29356797_18307.cpp:28:30: error: 'strcmp' was not declared in this scope
     return strcmp(a.num,b.num)<0;
                              ^