c misc

Author: asyncze

Diff for: c/misc/header-files.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+
+// filename.h
+/*
+    #ifndef FILENAME_H
+    #define FILENAME_H
+    
+    const int number = 10;
+
+    #endif
+*/
+
+#include "filename.h"
+
+int main() {
+    printf("%d\n", number); // 10
+}

Diff for: c/misc/linked-list.c

@@ -0,0 +1,90 @@
+// linked list implementation in C
+#include <stdio.h>
+#include <stdlib.h>
+
+// element is struct with a value and a pointer to the next element
+struct Element {
+    int value;
+    struct Element *next;
+};
+
+// allocate memory for element
+struct Element *create_element(int value) {
+    struct Element *element = (struct Element*) malloc(sizeof(struct Element));
+    
+    element->value = value;
+    element->next = NULL;
+    
+    return element;
+}
+
+// insert
+void ll_insert(struct Element **element, int value) {
+    struct Element *new_element = create_element(value);
+    // list is empty
+    if (*element == NULL) { *element = new_element; }
+    // list is not empty
+    else {
+        struct Element *current = *element;
+        // iterate until last element
+        while (current->next != NULL) {
+            current = current->next;
+        }
+        // insert new element
+        current->next = new_element;
+    }
+}
+
+// remove
+void ll_remove(struct Element **element, int value) {
+    struct Element *current = *element;
+    struct Element *previous = NULL;
+    // iterate until last element
+    while (current != NULL) {
+        // value is found
+        if (current->value == value) {
+            // value is first element
+            if (previous == NULL) {
+                *element = current->next;
+            }
+            // value is not first element
+            else {
+                previous->next = current->next;
+            }
+            // free memory
+            free(current);
+            return;
+        }
+        // update pointers
+        previous = current;
+        current = current->next;
+    }
+}
+
+// print
+void print(struct Element *element) {
+    struct Element *current = element;
+    // iterate until last element
+    while (current != NULL) {
+        printf("%d\n", current->value);
+        current = current->next;
+    }
+}
+
+int main() {
+    struct Element *ll = NULL;
+    
+    // insert
+    ll_insert(&ll, 5);
+    ll_insert(&ll, 10);
+    ll_insert(&ll, 15);
+    ll_insert(&ll, 20);
+    ll_insert(&ll, 25);
+    ll_insert(&ll, 30);
+    print(ll); // 5 10 15 20 25 30
+
+    // remove
+    ll_remove(&ll, 15);
+    ll_remove(&ll, 30);
+    print(ll); // 5 10 20 25
+}

Diff for: c/misc/macros.c

@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <stddef.h>
+
+// stringify error messages
+#define  error_message(error) \
+   printf("error: " #error "\n")
+
+// if not defined (used in header files to avoid multiple inclusion)
+#ifndef MESSAGE
+#define MESSAGE "This is the message if not already defined."
+#endif
+
+// parameterized macros
+#define square(x) ((x) * (x))
+#define max(x, y) ((x) > (y) ? (x) : (y))
+
+int main() {
+   printf("%s\n", __FILE__); // macros.c
+   printf("%s\n", __DATE__); // Aug 21 2019
+   printf("%s\n", __TIME__); // 01:22:18
+   printf("%d\n", __LINE__); // 12
+   printf("%d\n", __STDC__); // 1
+
+   error_message("This is an error.");
+   // error: "This is an error."
+
+   printf("%s\n", MESSAGE);
+   // This is the message if not already defined.
+
+   printf("%d\n", square(2)); // 4
+   printf("%d\n", max(4,5)); // 5
+}

Diff for: c/misc/memory.c

@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/*
+    - allocate an array of n elements of size s
+        void *calloc(int n, int s);
+
+    - release a block of memory at address
+        void free(void *address);
+
+    - allocate an array of b bytes (uninitialised)
+        void *malloc(int b);
+
+    - re-allocate memory at address (extending to new size s)
+        void *realloc(void *address, int s);
+*/
+
+int main() {
+    char name[36];
+    char *description; // pointer to char without size limit
+
+    // copy string of 35 bytes into buffer of 36 bytes
+    strcpy(name, "Wolfeschlegelsteinhausenbergerdorff");
+
+    // allocate memory dynamically (can result in fragmented memory)
+    // description = malloc(10 * sizeof(char));
+    // strcpy(description, "A too long text to store in only 10 bytes...");
+    // printf("%s\n", description);
+    // malloc(): corrupted top size
+    // Aborted
+
+    description = malloc(100 * sizeof(char));
+    strcpy(description, "A too long text to store in only 10 bytes...");
+    printf("%s\n", description);
+    // A too long text to store in only 10 bytes...
+
+    // free memory
+    free(description);
+}

Diff for: c/misc/pointers.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include <stddef.h>
+
+int main() {
+    int num = 5;
+    int *ip = NULL; // null pointer
+
+    printf("%p\n", ip); // 0x0 (nil)
+
+    // point to address of num
+    ip = &num;
+
+    printf("%p\n", &num); // 0x7ffdb78c2664
+    printf("%p\n", ip); // 0x7ffdb78c2664
+
+    // dereference (get value at address)
+    printf("%d\n", *ip); // 5
+}

Diff for: c/misc/valist.c

@@ -0,0 +1,26 @@
+#include <stdio.h>
+#include <stdarg.h>
+
+// declare function (normally in header file)
+double average(int n, ...);
+// define function
+double average(int n, ...) {
+    va_list valist; /* stdarg.h */
+    // return value
+    double sum = 0.0;
+    // init valist for n arguments
+    va_start(valist, n);
+    // access arguments
+    for (int i=0; i<n; i++) {
+        sum += va_arg(valist, int);
+    }
+    // free memory
+    va_end(valist);
+    // success
+    return sum / n;
+}
+
+int main() {
+    printf("average of {1,2,3,4,5}: %f\n", average(5, 1, 2, 3, 4, 5));
+    // average of {1,2,3,4,5}: 3.000000
+}