karlsson@karlsson-laptop:~/poly$ make
gcc -g -pedantic -std=c99 -Wall -Werror   -c -o poly.o poly.c
poly.c:14: error: conflicting types for ‘poly_t’
poly.h:4: error: previous declaration of ‘poly_t’ was here
poly.c:25: error: conflicting types for ‘new_poly_from_string’
poly.h:6: error: previous declaration of ‘new_poly_from_string’ was here
poly.c:47: error: conflicting types for ‘free_poly’
poly.h:7: error: previous declaration of ‘free_poly’ was here
poly.c:51: error: conflicting types for ‘poly_to_string’
poly.h:9: error: previous declaration of ‘poly_to_string’ was here
poly.c:56: error: conflicting types for ‘add’
poly.h:11: error: previous declaration of ‘add’ was here
poly.c:61: error: conflicting types for ‘mul’
poly.h:12: error: previous declaration of ‘mul’ was here
poly.c:65: error: conflicting types for ‘print_poly’
poly.h:14: error: previous declaration of ‘print_poly’ was here
cc1: warnings being treated as errors
poly.c:70: warning: return type of ‘main’ is not ‘int’
make: *** [poly.o] Error 1
karlsson@karlsson-laptop:~/poly$