C Programming: How to read input byte at a time and output only integers as tokens? -

i'm new c programming , have write program picks integers standard input , output them tokens. else should outputted "illegal". i'm not permitted use arrays or malloc, , declare ints or long ints. must use getchar() input , printf() output , nothing else. question is, how read input byte @ time, convert them tokens , check if ints?

for example: if input is:

hello 45 world thank 67 

it should output:

illegal 45 illegal illegal 67 illegal 

#include <stdio.h> #include <ctype.h> #include <limits.h>  int main() {     int ch;     int n;     int takenum, sign;     long long int wk;//long long int int64      wk=0ll;     takenum = 0;//flag     sign = 1;//minus:-1, other:1     while(eof!=(ch=getchar())){         if(ch == '-'){             sign = -1;             continue;         }         if(ch >= '0' && ch <= '9'){             if(takenum >= 0)                 takenum = 1;             else                 continue;             wk = wk * 10 + (ch - '0')*sign;             if(int_max < wk || int_min > wk){//overflow                 takenum = -1;//for skip             }             continue;         }         //space character continuing "illegal"         if(ch == ' ' || ch == '\t' || ch == '\n'){             if(takenum <= 0)                 printf("illegal\n");             else                 printf("%d\n", n=wk);             wk=0ll; takenum=0; sign=1;//reset         }     }     return 0; }