recursion - C Converting 4 digit numbers to binary -

i want print binary equivalent of numbers file in 20 bit field spaces after every 4 bits when number exceeds 1024 (i've tested this), no longer outputs in binary in base don't know (i.e. 1234 = 0000 0014 1006 5408)

here code

#include <stdio.h> long converttobinary(long);  int main() {     char binnum[20]; //binary number char array     int i;     long b, decnum; //b output binary number, decnum each input number file     file *fileptr;     fileptr = fopen("numbers.txt", "r");     while (!feof(fileptr))     {         fscanf(fileptr, "%li", &decnum);         if (decnum < 0  || decnum > 65535)         {             printf("error, %5li out of range.\n", decnum);             continue;         }         b = converttobinary(decnum); //function call binary conversion          = 18;         while (i >= 0)         {             if (i == 4 || == 9 || == 14)             {                 binnum[i] = ' ';             }             else if (b != 0)             {                 binnum[i] = b % 10 + '0';                 b /= 10;             }             else              {                 binnum[i] = '0';             }             i--;         }         binnum[19] = '.';         printf("the binary representation of %5li is: ", decnum);         (i = 0; i<20; i++)         {             printf("%c", binnum[i]);         }         printf("\n");     }  return 0; }  //recursion function long converttobinary(long number) {     if (number == 0)     {         return 0;     }     else     {         return (number % 2 + 10 * converttobinary(number / 2));     } } 

the file numbers.txt has numbers : 0 1 2 3 16 17 1234 5678 65535

your converttobinary function producing decimal-coded-binary (as opposed binary-coded-decimal) uses decimal digit per bit.

it looks long has same range int on system, i.e. 2³¹, covers ten decimal digits. once eleventh digit, overflow.

switching unsigned long long, has 64 bits, fix problem. however, sub-optimal: better off writing to-binary conversion writes zeros , ones array of chars provide. can recursively if you'd like, iterative solution fine.

note to-binary conversion not need insert spaces char array. can done main function.