Since the input sounds like it is tightly formatted, I would recommend using fscanf to read each "number" as text. The %s specifier is whitespace delimited, so it will skip the intervening whitespace. Then checking that the second "digit" is a '1' is trivial.
Code:
#include <stdio.h>
int main()
{
static const char filename[] = "file.txt";
FILE *file = fopen(filename, "r");
if ( file != NULL )
{
char text[5];
while ( fscanf(file, "%4s", text) == 1 )
{
if ( text[1] == '1' )
{
puts(text);
}
}
fclose(file);
}
else
{
perror(filename);
}
return 0;
}
/* file.txt
11 111 1678 1334 1445 1335 1225 72 62 42 54 544 944 9111 9191
*/
/* my output
11
111
9111
9191
*/