View Compilation Error

In file included from 0_0_18671561_16512.cpp:1:0:
0_0_18671561_16512.cpp: In function 'int main()':
0_0_18671561_16512.cpp:6:25: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
     while(gets(Cipher)!=EOF)
                         ^
0_0_18671561_16512.cpp:8:26: error: 'strlen' was not declared in this scope
         len=strlen(Cipher);
                          ^
0_0_18671561_16512.cpp:10:33: error: 'strcmp' was not declared in this scope
         if(strcmp(Cipher,"START")==0)
                                 ^