Elvin’s C Quiz

This is a succinct quiz to test your C language programming performance.

Rookie Warning : NO EASY SHIT HERE

1. Pseudo Random Number Generator

/** in 32bit or 64bit environment **/
#include <stdlib.h>
#include <stdio.h>

#define RANGE 4

int main(int argc, char** argv) {
    int count[RANGE] = {0};

    for (int i = 0; i < 1000000; i++) {
        int r = rand() % 8;

        r %= RANGE;

        count[r]++;
    }

    for (int i = 0; i < RANGE; i++)
        printf("%d ", count[i]);
    putchar('\n');
    return 0;
}

Q1: What does this program do?

Q2: What is the most likely distribution of the output line?

Q3: If 3 and then 5 are set to the RANGE macro, what distribution would them be?

Code Snippet Changed

From

        int r = rand() % 8;

        r %= RANGE;

To

        int r = rand() % RANGE;

Q4: What is the distribution now for 4, 3 and 5?

Q5: Can you explain the difference?

2. Linked List

struct linked_list{
    struct linked_list *next;
    int val;
};
/*
 * This function finds one and delete one, then returns the modified list
 */
struct linked_list* delete_one_by_val(struct linked_list* head, int val) {
    if (head->val != val && NULL != head)
        return delete_one_by_val(head->next, val);
    else if (NULL != head)
        return head->next;

    return NULL;
}

Q1: How many bug(s) have you found and where are they?

Hint: Consider calling this function frequently during same runtime.

Q2: Can you modified this function so it can find all the matching node and delete them?