The program includes the following main function: int main() { char str1[20], str2[80]; scanf("%s%s", str1, str2); printf("%d\n", occurrence1(str1, str2)); printf("%d\n", occurrence2(str1, str2)); return 0; } The program also includes two occurrence functions: occurrence1 and occurrence2. int occurrence#(char *sub, char *str)/* # is 1 or 2*/ is the function that finds number of occurrences of sub in str. For example, a)occurrence1("ab","abc") returns 1; b)occurrence1("ab","bac") returns 0; c)occurrence1("aba","ababa") returns 2; Occurrence1 is a recursive function, occurrence2 is non-recursive function.

Based on the given requirements, here's the implementation of the two occurrence functions (`occurrence1` and `occurrence2`) in C:

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

int occurrence1(char *sub, char *str) {
    if (*str == '\0')
        return 0;
    else if (strncmp(sub, str, strlen(sub)) == 0)
        return 1 + occurrence1(sub, str + strlen(sub));
    else
        return occurrence1(sub, str + 1);
}

int occurrence2(char *sub, char *str) {
    int count = 0;
    int sub_len = strlen(sub);
    int str_len = strlen(str);

    for (int i = 0; i <= str_len - sub_len; i++) {
        if (strncmp(sub, str + i, sub_len) == 0)
            count++;
    }

    return count;
}

int main() {
    char str1[20], str2[80];
    scanf("%s%s", str1, str2);
    printf("%d\n", occurrence1(str1, str2));
    printf("%d\n", occurrence2(str1, str2));
    return 0;
}

In this program, the `occurrence1` function uses recursion to find the number of occurrences of `sub` in `str`. It checks if the current substring of `str` matches the `sub` string. If there is a match, it increases the count by 1 and recursively calls `occurrence1` on the remaining part of `str`. If there is no match, it recursively calls `occurrence1` on `str` excluding the first character.

The `occurrence2` function is a non-recursive alternative that uses a loop to iterate over `str` and compare substrings of length `sub_len` with `sub`. It increases the count whenever a match is found.

The main function reads two strings from input using `scanf` and then calls `occurrence1` and `occurrence2` functions respectively to find the occurrences of `str1` in `str2`, printing the results using `printf`.

Please note that the program assumes the input strings (`str1` and `str2`) are null-terminated strings.