C/C++ reading line at a time - c++

Question

I was trying to solve a programming problem of some site and this one had the following statement:
Read a string and parse it as a number, char 'l' can be considered as number 1 and chars 'o' and 'O' can be considered as number 0, commas and spaces will be accepted in the input but ignored, if any other character is found then output error...
So... since there can be spaces in the lines, I used gets (the documentation says it removes the new line and puts a terminator)...
My sequence of IF test if it is a number, then if its an acceptable letter, then checks if it is not a comma or a space... And I found out that it was almost always entering in the last IF even though there wasn't any character that should lead it there so I changed the printf inside it to print the
printf("%d error", st[k]);
And it outputs 13: carriage return... I tried this compiler here
#include <cstdio>
#include <cstring>
#include <cstdlib>
int main()
{
char st[100];
char buf[100];
int k, i;
long long int num;
ops: while(gets(st))
{
for(k = i = 0; st[k]; k++)
if(st[k] >= '0' && st[k] <= '9')
buf[i++] = st[k];
else if(st[k] == 'o' || st[k] == 'O')
buf[i++] = '0';
else if(st[k] == 'l')
buf[i++] = '1';
else if(st[k] != ',' && st[k] != ' ')
{
printf("error\n");
goto ops;
}
// remaining code comes here...
}
The input sample had the following lilnes:
lo6
234,657
hi
,,,,,5,,5, 4
2200000000
00
Should I use other function to read instead?
Any suggestions on how to avoid this damn Carriage Return?
The statemente for the problem can be seen here if you want more detail
Thanks
EDIT:
I'm asking that because there seem to be a difference between the compiler I'm using and the compiler the website was using, once I submitted a code that wasn't generating the correct output on mine but I thought the code was correct... and it passed. Then after it, I tried the code on a linux virtual machine and also correct but my gcc on windows failed... some characters were completely away from where they should be
The thing is:

Answer 1

The preferred method of line input is getline. If you do not know the width of the input beforehand, getline will allocate space for you if you set the buffer pointer to NULL.
Since you indicate you have some experience in C, the following will show you how to step through an input string and parse it in the manner you want. While there are many ways to handle parsing strings, it is hard to beat assigning a pointer to the beginning of the string and then advancing down the string until you reach the null-terminating character (unsigned 0, or char '\0'). If you have any questions after looking it over, just ask:
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char *argv[]) {
char *buffer = NULL;
size_t n = 0;
ssize_t len;
char *ptr = NULL;
char *output = NULL;
int idx = 0;
printf ("\nEnter your string below: ([ctrl + d] on blank line to end)\n");
while ((len = getline (&buffer, &n, stdin)) != -1) {
ptr = buffer;
idx = 0;
output = malloc (sizeof (char) * len);
while (*ptr != 0) {
if (*ptr >= 48 && *ptr <= 57) output [idx++] = *ptr;
if (*ptr == 'I') output [idx++] = '1';
if (*ptr == 'o' || *ptr == 'O') output [idx++] = '0';
ptr++;
}
output [idx] = 0;
printf ("\n valid output: %s\n\n", output);
free (output);
}
return 0;
}
output:
Enter your string below: ([ctrl + d] on blank line to end)
This sting has 12345 aeiou AEIOU,,,,,commas, and 99, to end.
valid output: 123450100990