reading unknown number of of integers and printing them in words - c

Question

I'm trying to process input from stdin but keep running into walls.
My goal is to read a strem of numbers(0-99) and print each one in words.
My first attempt was:
int main(void) {
char *a[20] = {"zero","one","two","three","four","five","six","seven","eight",
"nine","ten","eleven","twelve","thirteen","fourteen","fifteen","sixteen",
"seventeen","eighteen","nineteen"};
char *b[8] = {"twenty","thirty","fourty","fifty","sixty","seventy","eighty","ninety"};
int num=0, tens=0, ones=0;
while (scanf("%d", &num)==1){
tens = num/10;
ones = num%10;
if (tens>1){
printf("%s ", b[tens-2]);
printf("%s \n", a[ones]);
}
else
printf("%s \n", a[num]);
}
printf("done");
return 0;
}
Output is correct but scanf never terminates the loop.
Second attempt:
int main(void) {
char *a[20] = {"zero","one","two","three","four","five","six","seven","eight",
"nine","ten","eleven","twelve","thirteen","fourteen","fifteen","sixteen",
"seventeen","eighteen","nineteen"};
char *b[8] = {"twenty","thirty","fourty","fifty","sixty","seventy","eighty","ninety"};
char line[1024], *ptr = NULL;
long num;
int tens=0, ones=0;
if(fgets(line, sizeof(line), stdin)!=NULL){
do {
num = strtol(line, &ptr, 10);
tens = num/10;
ones = num%10;
if (tens>1){
printf("%s ", b[tens-2]);
printf("%s \n", a[ones]);
}
else
printf("%s \n", a[num]);
}while (*ptr!= '\n');
}
printf("done");
return 0;
}
Here I get a compilation error and can't find the problem so I don't know if it works.
[UPDATE]: The second code runs but for an input of more then one number like
12 35 51 it prints the first number (twelve) infinitely.
Any help would be greatly appreciated.

Answer 1

You are so close. You just need to validate the return of strtol, and update the pointer address based on the endptr following the call to strtol. You should also check for values outside the range of your conversion as mentioned in the discussion. This is all that is needed:
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
int main(void) {
char *a[] = {"zero","one","two","three","four","five","six",
"seven","eight","nine","ten","eleven","twelve",
"thirteen","fourteen","fifteen","sixteen",
"seventeen","eighteen","nineteen"};
char *b[] = {"twenty","thirty","fourty","fifty","sixty",
"seventy","eighty","ninety"};
char line[1024] = "";
long num;
int tens=0, ones=0;
if (fgets (line, sizeof(line), stdin) != NULL) {
char *p = line, *ep = NULL;
errno = 0;
while (errno == 0) {
num = strtol (p, &ep, 10); /* convert to long */
if (p == ep) break; /* no digits, break */
p = ep; /* update p to ep */
if (num < 0 || 99 < num) { /* validate range */
fprintf (stderr, "error: %ld - out of range.\n", num);
continue;
}
tens = num/10;
ones = num%10;
if (tens > 1) {
printf ("%s ", b[tens-2]);
printf ("%s \n", a[ones]);
}
else
printf("%s \n", a[num]);
}
}
printf ("done\n");
return 0;
}
Example Use/Output
$ ./bin/n2string
12 55 61 -1 33 102 4
twelve
fifty five
sixty one
error: -1 - out of range.
thirty three
error: 102 - out of range.
four
done
Look it over and let me know if you have any questions.

Answer 2

The purpose of the code appears to be to print the text version of a digit that was entered. Your code works almost unchanged, I just added a library and ran it.
#include <stdio.h>
#include <stdlib.h>
int main(void) {
char *a[20] = {"zero","one","two","three","four","five","six","seven","eight",
"nine","ten","eleven","twelve","thirteen","fourteen","fifteen","sixteen",
"seventeen","eighteen","nineteen"};
char *b[8] = {"twenty","thirty","fourty","fifty","sixty","seventy","eighty","ninety"};
char line[1024], *ptr = NULL;
long num;
int tens=0, ones=0;
if(fgets(line, sizeof(line), stdin)!=NULL){
do {
num = strtol(line, &ptr, 10);
tens = num/10;
ones = num%10;
if (tens>1){
printf("%s ", b[tens-2]);
printf("%s \n", a[ones]);
}
else
printf("%s \n", a[num]);
}while (*ptr!= '\n');
}
printf("done");
return 0;
}
Test
19
nineteen
done
Maybe the problem was that you didn't know the purpose of the code.