#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>

typedef struct {
    const char* text;
    unsigned    text_len;
    unsigned    text_pos;

    const char* token;
    unsigned    token_len;
} lexer_t;

bool lexer_next_token(lexer_t* self)
{
    unsigned i;
    unsigned len;
    char     ch;

    for(i = self->text_pos, len = 0;
        i != self->text_len;
        i++, len++) {

        ch = self->text[i];

        if((ch < 'A' || ch > 'Z') &&
           (ch < 'a' || ch > 'z')) {
            if(ch != ' ') {
                if(len == 0) {
                    self->token = &self->text[i];
                    self->token_len = 1;
                    self->text_pos = i + 1;
                    return true;
                }

                self->token = &self->text[i-len];
                self->token_len = len;
                self->text_pos = i;

                return true;
            } else {
                len = 0;
            }
        }
    }

    if(len) {
        self->token = &self->text[i-len];
        self->token_len = len;
        self->text_pos = i;
        return true;
    }

    return false;
}

int main(int argc, char* argv[])
{
    const char* text = "hello, world";
    lexer_t lexer = {0};

    lexer.text = text;
    lexer.text_len = strlen(text);

    while(lexer_next_token(&lexer)) {
        printf("%.*s\n",(int)lexer.token_len,lexer.token);
    }
}