three problems - C.c

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

int main()
{
    char txt[100], pat[100];
    int k, i, plen, b;

    gets(txt);
    gets(pat);

    plen = strlen(pat);
    b = 0;

    for(i = 0; txt[i] != '\0'; i++) {
        if(pat[0] == txt[i]) {
            for(k = 1; pat[k] != '\0'; k++) {
                if(pat[k] != txt[i+k])
                    break;
                if(k == plen-1) {
                    if(!b) {
                        printf("Pattern found at position: %d", i+1);
                        b = 1;
                    }
                    else
                        printf(", %d", i+1);
                }
            }
        }
    }

    if(!b)
        puts("Not found!");

    return 0;
}