foo.cpp: In function 'long int operation(long int, long int, long int)':
foo.cpp:12:7: warning: unused variable 'x' [-Wunused-variable]
  long x,s;
       ^
foo.cpp:12:9: warning: unused variable 's' [-Wunused-variable]
  long x,s;
         ^
foo.cpp: In function 'int main()':
foo.cpp:84:14: error: 'strlen' was not declared in this scope
   l=strlen(ch);
              ^
foo.cpp: In function 'long int operation(long int, long int, long int)':
foo.cpp:18:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^