feat: add listprimes

listprimes/includes/linkedlist.h

@@ -0,0 +1,18 @@
+/* Contains code to create and manipulate a linked list of `int`s */
+
+typedef struct elem {
+    int val;
+    struct elem* next;
+} elem;
+
+elem* create(int val, elem* prev_elem);
+    // Add a new elem number to the linked list
+
+void display(elem* first_elem);
+    // Print out the current list of elems
+
+void release(elem* first_elem);
+    // Release the memory used by the linked list
+
+int check_membership(int val, elem* first_elem);
+    // Check linked list for presence of `val`

listprimes/includes/listprimes.h

@@ -0,0 +1,13 @@
+/* Contains code to create a linked list of prime numbers. */
+
+elem* first_n_primes(int n);
+    // Return a pointer to the first element in a linked list of the first n
+    // primes
+
+elem* primes_lte_n(int n);
+    // Return a pointer to the first element in a linked list of all primes
+    // less than or equal to `n`
+
+int is_prime(int x, elem* first_prime);
+    // Check if x is prime, given a linked list of prime numbers (assumed
+    // valid)

listprimes/linkedlist.c

@@ -0,0 +1,50 @@
+/* Contains code to create and manipulate a linked list of `int`s */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "linkedlist.h"
+
+elem* create(int val, elem* prev_elem) {
+    // Add a new elem number to the linked list
+    elem* new_elem = malloc(sizeof(elem));
+    new_elem->val = val;
+    new_elem->next = NULL;
+    if (prev_elem != NULL) prev_elem->next = new_elem;
+    return new_elem;
+}
+
+void display(elem* first_elem) {
+    // Print out the current list of elems
+    elem* cur_elem = first_elem;
+    int i = 1;
+    while (cur_elem != NULL) {
+        printf("(%i) %i\n", i, cur_elem->val);
+        cur_elem = cur_elem->next;
+        i++;
+    }
+}
+
+void release(elem* first_elem) {
+    // Release the memory used by the linked list
+    elem *cur_elem = first_elem, *next_elem;
+    while (cur_elem != NULL) {
+        next_elem = cur_elem->next; // Store pointer to next elem
+        free(cur_elem); // release memory for the current elem
+        cur_elem = next_elem; // next iteration, free the next elem
+    }
+}
+
+int check_membership(int val, elem* first_elem) {
+    // Check linked list for presence of `val`
+    int found_val = 0;
+    elem* cur_elem = first_elem;
+    while (cur_elem != NULL) {
+        if (val == cur_elem->val) {
+            found_val = 1;
+            break;
+        } else {
+            cur_elem = cur_elem->next;
+        }
+    }
+    return found_val;
+}

listprimes/listprimes.c

@@ -0,0 +1,57 @@
+/* Contains code to create a linked list of prime numbers. */
+
+#include <stdlib.h>
+#include <math.h>
+#include "linkedlist.h"
+#include "listprimes.h"
+
+elem* first_n_primes(int n) {
+    // Return a pointer to the first element in a linked list of the first n
+    // primes
+
+    elem *first_prime = create(2, NULL), *cur_prime = first_prime;
+    int cur_val = 3, list_len = 1;
+    
+    // Iterate until list of primes is desired length
+    while (list_len < n) {
+        if (is_prime(cur_val, first_prime)) { // cur_val is prime
+            cur_prime = create(cur_val, cur_prime); // add to linked list
+            list_len ++;
+            // printf("(%i) %i\n", list_len, cur_val);
+        }
+        cur_val += 2;
+    }
+    return first_prime;
+}
+
+elem* primes_lte_n(int n) {
+    // Return a pointer to the first element in a linked list of all primes
+    // less than or equal to `n`
+    elem *first_prime = create(2, NULL), *cur_prime = first_prime;
+    int cur_val = 3, list_len = 1;
+    
+    // Iterate until all primes less than n have been considered
+    while (cur_val <= n) {
+        if (is_prime(cur_val, first_prime)) { // cur_val is prime
+            cur_prime = create(cur_val, cur_prime); // add to linked list
+            list_len ++;
+            // printf("(%i) %i\n", list_len, cur_val);
+        }
+        cur_val += 2;
+    }
+    return first_prime;
+}
+
+int is_prime(int x, elem* first_prime) {
+    // Check if x is prime, given a linked list of prime numbers (assumed
+    // valid)
+    elem* cur_prime = first_prime;
+    double sqrtx = sqrt((double)x);
+    // Iterate through each element of the linked list
+    while (cur_prime != NULL) {
+        if (x % cur_prime->val == 0) return 0;
+        else if (cur_prime->val > sqrtx) return 1;
+        else cur_prime = cur_prime->next;
+    }
+    return 1;
+}

listprimes/main.c

@@ -0,0 +1,56 @@
+/* Compile and run using:
+gcc listprimes.c linkedlist.c main.c -o list-primes && list-primes 0 100
+
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "linkedlist.h"
+#include "listprimes.h"
+
+typedef enum {FIRST_N_PRIMES, PRIMES_LTE_N} mode_type;
+const int DEFAULT_MODE = FIRST_N_PRIMES; // by default, list first n primes
+const int DEFAULT_N = 20; // by default, list first 20 primes
+
+int main(int argc, char** argv) {
+    // Read arguments / use defaults
+    mode_type mode;
+    int n;
+    switch (argc) {
+        case 1: // no args provided, use defaults
+            mode = DEFAULT_MODE;
+            n = DEFAULT_N;
+            break;
+        case 2: // 1 arg, use default mode and custom n
+            mode = DEFAULT_MODE;
+            n = atoi(argv[1]);
+            break;
+        case 3: // custom args, check validity
+            mode = (mode_type) atoi(argv[1]);
+            n = atoi(argv[2]);
+            break;
+        default: // error
+            fprintf(stderr, "Error: Please enter valid arguments\n");
+            return 1;
+    }
+
+    // Create appropriate list of primes
+    elem* prime_list;
+    switch (mode) {
+        case FIRST_N_PRIMES:
+            prime_list = first_n_primes(n);
+            break;
+        case PRIMES_LTE_N:
+            prime_list = primes_lte_n(n);
+            break;
+        default:
+            fprintf(stderr, "Error: Invalid mode type\n");
+            return 2;
+    }
+    
+    // Display list of primes and release memory
+    display(prime_list);
+    release(prime_list);
+
+    return 0;
+}

listprimes/makefile

@@ -0,0 +1,20 @@
+#target: dependency_1 dependency_2 dependency_3 ...
+#	command
+#
+RM = /bin/rm -f
+OBJ = main.o listprimes.o linkedlist.o
+#
+list-primes: $(OBJ)
+	gcc $(OBJ) -o list-primes -lm
+#
+linkedlist.o: linkedlist.c includes/linkedlist.h
+	gcc -I ./includes -c linkedlist.c -o linkedlist.o
+#
+listprimes.o: listprimes.c includes/linkedlist.h includes/listprimes.h
+	gcc -I ./includes -c listprimes.c -o listprimes.o
+#
+main.o: main.c includes/linkedlist.h includes/listprimes.h
+	gcc -I ./includes -c main.c -o main.o
+#
+clean:
+	$(RM) $(OBJ) list-primes *~

listprimes/readme.md

@@ -0,0 +1,22 @@
+[source](https://gist.github.com/jakelevi1996/ce46a808fe3b5ef06ece63aea0bd2fed)
+
+* build
+
+```
+/usr/bin/gcc main.c listprimes.c linkedlist.c -o list-primes -lm
+```
+
+* build in two steps (object files, executable file)
+
+```
+gcc -c main.c -I ./includes
+gcc -c listprimes.c -I ./includes
+gcc -c linkedlist.c -I ./includes
+gcc main.o listprimes.o linkedlist.o -o list-primes -lm
+```
+
+* run
+
+```
+./list-primes
+```