C :: Functions Retuning Non Integers

from k&r book (4.2 - functions retuning non integers)
(doesnt compile - 1 error)

Code:

#include <stdio.h>
#define MAXLINE 100
/* rudimentary calculator */
main()
{
double sum, atof(char []);
char line[MAXLINE];
int getline(char line[], int max);
sum = 0;
while (getline(line, MAXLINE) > 0)
printf(" %g
", sum += atof(line));
return 0;
}

Code:

int getline(char line[], int max); is no different from:

Code:

getline(char line[], int max); ?

so, the int (return type) is optional when using a function. i assume return type is casted double? why the (char [])? just weird cuz i never seen it before