turboc++ - Program compiles and executes without header files turbo c++ -


i'm noob in programming. teacher compiled program without pre-processor directive @ , executed , displayed output. hello world program. i'm confused without directives how able carry out "printf" function.

in "classic" ansi c (c89/90) can call non-variadic functions without pre-declaring them, long careful supplying arguments of proper type. so, if 1 properly, 1 can write formally valid c89/90 program not include standard headers. e.g.

int main() {   puts("hello world");   return 0; }

in modern c not possible, since starting c99 functions have declared before being called.

now, calling printf without pre-declaring (with prototype) caused undefined behavior in c89/90, since printf variadic function. so, if teacher did 

int main() {   printf("hello world\n");   return 0; }

then he/she still has lot learn c. c89/90 program not valid, if compiled, executed , displayed output "looked fine" you.

however, can still pre-declare function manually

​int printf(const char *format, ...);​  int main() {   printf("hello world\n");   return 0; }

and end valid c89/90 program not use preprocessing directives. doing way not programming practice though.


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