+9-double-pointers/

9-double-pointers/CMakeLists.txt

@@ -0,0 +1,10 @@
+add_executable(selection-sort-ints selection-sort.c)
+add_executable(selection-sort-strings selection-sort-strings.c)
+
+add_executable(scores scores.c)
+
+add_executable(echo echo.c)
+
+add_executable(pointers-malloc pointers-malloc.c)
+
+add_executable(decl decl.c)

9-double-pointers/README.md

@@ -0,0 +1,20 @@
+# 10-double-pointers
+
+## `selection-sort-strings.c`
+
+- `const`
+
+## `echo.c`
+
+- Linux `echo`
+- C standard
+- `printf("%s\n", argv[i])`: printf the nullptr
+
+## `scores.c`
+
+- `student_score_table`: as a 2D array
+- `Print`
+  - `int table[][COLS]` vs. `int (*table)[COLS]`
+- `malloc`
+  - `int *`
+  - `int (*)[COLS]`

9-double-pointers/decl.c

@@ -0,0 +1,21 @@
+// Created by hengxin on 11/27/2024.
+
+int main() {
+  char **argv;
+
+  int *names[10];
+
+  int (*musician_score_table)[10];
+
+  int *StrCpyStd(char *dest, const char *src);
+
+  int (*comp)(const void *left, const void *right);
+
+  int atexit(void (*func)(void));
+
+  void (*signal(int sig, void (*handler)(int)))(int);
+
+  char (*(*func(int num, char *str))[])();
+
+  char (*(*arr[3])())[5];
+}

9-double-pointers/echo.c

@@ -0,0 +1,50 @@
+/**
+ * Echo program (command-line) arguments.
+ *
+ * Created by hengxin on 11/27/2024.
+ */
+
+#include <stdio.h>
+
+// arg: argument
+// c: count
+// v: vector
+
+// argv[0]: the name of the program
+// argv[1 .. argc - 1]: command line arguments
+// argv[argc]: NULL
+int main(int argc, char *argv[]) {
+  // for version with argv
+  // for (int i = 1; i < argc; ++i) {
+  //   printf("argv[%d] = %s\n", i, argv[i]);
+  // }
+
+  // for version with pointers
+  // for (char **ptr = argv + 1; *ptr != NULL; ptr++) {
+  //   printf("%s\n", *ptr);
+  // }
+
+  // while version
+  // char **ptr = argv + 1;
+  // while (*ptr != NULL) {
+  //   printf("%s\n", *ptr);
+  //   ptr++;
+  // }
+
+  // WRONG
+  // char **ptr = argv + 1;
+  // while (*ptr++ != NULL) {
+  //   printf("%s\n", *ptr);
+  // }
+
+  char **ptr = argv;
+  // *++ptr
+  // *ptr++
+  // *--ptr
+  // *ptr--
+  while (*++ptr != NULL) {
+    printf("%s\n", *ptr);
+  }
+
+  return 0;
+}

9-double-pointers/pointers-malloc.c

@@ -0,0 +1,142 @@
+// Created by hfwei on 2024/11/27.
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define LEN 3
+#define ROW 3
+#define COL 4
+
+int main(void) {
+  // (1) One-Dimensional Array
+  // Visualization: https://tinyurl.com/pointers-malloc-int
+
+  // malloc
+  int *array = malloc(LEN * sizeof *array);
+  if (array == NULL) {
+    printf("malloc failed\n");
+    return EXIT_FAILURE;
+  }
+
+  // fill in
+  for (int i = 0; i < LEN; ++i) {
+    array[i] = i * i;
+  }
+
+  // print
+  for (int i = 0; i < LEN; ++i) {
+    printf("%d ", array[i]);
+  }
+  printf("\n\n");
+
+  // free
+  free(array);
+
+  // (2) Two-Dimensional Array
+  // Visualization: https://tinyurl.com/pointers-malloc-int-array
+
+  // malloc
+  int (*table)[COL] = malloc(ROW * sizeof *table);
+
+  // fill in
+  for (int i = 0; i < ROW; ++i) {
+    for (int j = 0; j < COL; ++j) {
+      table[i][j] = i * j;
+    }
+  }
+
+  // print
+  for (int i = 0; i < ROW; ++i) {
+    for (int j = 0; j < COL; ++j) {
+      printf("%d ", table[i][j]);
+    }
+    printf("\n");
+  }
+  printf("\n");
+
+  // free
+  free(table);
+
+  // (3) One-Dimensional Array of Pointers
+  // Visualization: https://tinyurl.com/pointers-malloc-arraypointers
+
+  // malloc and fill in
+  int *array_of_pointers[LEN];
+  for (int i = 0; i < LEN; ++i) {
+    array_of_pointers[i] = malloc((i + 1) * sizeof *array_of_pointers[i]);
+    for (int j = 0; j < i + 1; ++j) {
+      array_of_pointers[i][j] = i * j;
+    }
+  }
+
+  // print
+  for (int i = 0; i < LEN; ++i) {
+    for (int j = 0; j < i + 1; ++j) {
+      printf("%d ", array_of_pointers[i][j]);
+    }
+    printf("\n");
+  }
+  printf("\n");
+
+  // free
+  for (int i = 0; i < LEN; ++i) {
+    free(array_of_pointers[i]);
+  }
+
+  // (4) Two-Dimensional Array with Potentially Non-Contiguous Memory
+  // Visualization: https://tinyurl.com/pointers-malloc-int-pp
+
+  // malloc
+  int **matrix = malloc(ROW * sizeof *matrix);
+  for (int i = 0; i < ROW; ++i) {
+    matrix[i] = malloc(COL * sizeof *matrix[i]);
+  }
+
+  // fill in
+  for (int i = 0; i < ROW; ++i) {
+    for (int j = 0; j < COL; ++j) {
+      matrix[i][j] = i * j;
+    }
+  }
+
+  // print
+  for (int i = 0; i < ROW; ++i) {
+    for (int j = 0; j < COL; ++j) {
+      printf("%d ", matrix[i][j]);
+    }
+    printf("\n");
+  }
+  printf("\n");
+
+  // free
+  for (int i = 0; i < ROW; ++i) {
+    free(matrix[i]);
+  }
+  free(matrix);
+
+  // (5) Two-Dimensional Array with Contiguous Memory
+  // Visualization: https://tinyurl.com/pointers-malloc-int-p
+
+  // malloc
+  int *matrix_contiguous = malloc(ROW * COL * sizeof *matrix_contiguous);
+
+  // fill in
+  for (int i = 0; i < ROW; ++i) {
+    for (int j = 0; j < COL; ++j) {
+      matrix_contiguous[i * COL + j] = i * j;
+    }
+  }
+
+  // print
+  for (int i = 0; i < ROW; ++i) {
+    for (int j = 0; j < COL; ++j) {
+      printf("%d ", matrix_contiguous[i * COL + j]);
+    }
+    printf("\n");
+  }
+
+  // free
+  free(matrix_contiguous);
+
+  return 0;
+}

9-double-pointers/scores.c

@@ -0,0 +1,78 @@
+// Created by hengxin on 11/27/2024.
+
+// Python Tutor Visualization:
+// (1) https://tinyurl.com/scores-of-musicians
+// (2) https://tinyurl.com/scores-of-musicians-malloc
+// https://tinyurl.com/
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define NUM_OF_MUSICIANS 4
+#define NUM_OF_SCORES 3
+
+void Print(const int table[][NUM_OF_SCORES], int num_of_musicians);
+
+int main() {
+  // C, Java, Python scores of several musicians
+
+  // TODO: (1) initialize scores with a 2D array
+  // const int scores[NUM_OF_MUSICIANS][NUM_OF_SCORES] = {
+  //     { 0, 10, 20 },
+  //     { 10, 20, 30 },
+  //     { 20, 30, 40 },
+  //     { 30, 40, 50 },
+  // };
+
+  // TODO: (2) Dynamically allocate memory for scores
+  // malloc here
+  int (*scores)[NUM_OF_SCORES] = malloc(NUM_OF_MUSICIANS * sizeof(*scores));
+  if (scores == NULL) {
+    return 0;
+  }
+
+  // fill in data here
+  for (int i = 0; i < NUM_OF_MUSICIANS; ++i) {
+    for (int j = 0; j < NUM_OF_SCORES; ++j) {
+      scores[i][j] = i * j;
+    }
+  }
+
+  // print it here
+  Print(scores, NUM_OF_MUSICIANS);
+
+  // ptr_scores here
+  int (*ptr_scores)[NUM_OF_SCORES] = scores;
+  printf("ptr_scores[3][2] = %d\n",
+         (*(ptr_scores + 3))[2]);
+
+  // do not forget to free it
+  free(scores);
+
+  return 0;
+}
+
+// table: int table[][COL]
+// int table[]: int *table
+// int table[][COL]: int (*table)[COL]
+void Print(const int table[][NUM_OF_SCORES], int num_of_musicians) {
+  for (int i = 0; i < num_of_musicians; i++) {
+    for (int j = 0; j < NUM_OF_SCORES; j++) {
+      // table[i][j]: *(*(table + i) + j)
+      // table: int (*)[COL]
+      // table + i: int (*)[COL]
+      // *(table + i): int *
+      // *(table + i) + j: int *
+      // *(*(table + i) + j): int
+      printf("table[%d][%d]: %d\n\n",
+             i, j, table[i][j]);
+
+      printf("table: %p\n", table);
+      printf("table + %d: %p\n", i, table + i);
+      printf("*(table + %d): %p\n", i, *(table + i));
+      printf("*(table + %d) + %d: %p\n", i, j, *(table + i) + j);
+      printf("*(*(table + %d) + %d): %d\n", i, j, *(*(table + i) + j));
+    }
+    printf("\n\n");
+  }
+}