Script started on Mon Oct 12 17:28:57 2026
macbook:C_ch11> cat addr_and_indirect.c 
/* 
  addr_and_indirect.c
*/
#include <stdio.h>

int main (void) {

  int i, j, *p = &i;
  i = 1;
  printf("i = %d\n", i);
  printf("*p = %d\n", *p);

  *p = 4;

  printf("i = %d\n", i);
  printf("*p = %d\n", *p);

  j = *&i;
  printf("j = %d\n", j);

  return 0;
}

macbook:C_ch11> gcc addr_and_indirect.c
macbook:C_ch11> echo predictions 1 1 4 4 4
predictions 1 1 4 4 4
macbook:C_ch11> ./a.out
i = 1
*p = 1
i = 4
*p = 4
j = 4
macbook:C_ch11> cat bad_avg_sum.c
    void avg_sum (float a[], int n, float *avg, float *sum)
    {
        int i;
        sum = 0.0;           //  *sum = 0.0
        for (i=0;i<n;i++)
            sum += a[i];     //  *sum = *sum + a[i]
        avg = sum / n;       //  *avg= *sum / n
    }

// This has problems
macbook:C_ch11> echo "what is the difference between   float b=3.0;  float *b=3.0;"
what is the difference between   float b=3.0;  float *b=3.0;
macbook:C_ch11> echo "float b1 = 3.0;"
float b1 = 3.0;
macbook:C_ch11> echo "float *b2;"
float *b2;
macbook:C_ch11> echo "*b2 = b1;"
*b2 = b1;
macbook:C_ch11> cd ~/Desktop
macbook:Desktop> cat avg_sum_v2.c 
#include <stdio.h>

void avg_sum (float a[], int n, float *avg, float *sum)
{
    int i;
    // This is the corrected version
    *sum = 0.0; // *sum = 0.0
    for (i=0;i<n;i++)
        *sum += a[i]; // *sum = *sum + a[i]
    *avg = *sum / n; // *avg= *sum / n
}

int main() {
    float a[] = {3.0, 4.5, 6.7};

    float avg, sum;
    int a_size = sizeof(a);

    avg_sum(a, a_size, &avg, &sum);

    // but the results do not make sense.
    printf(" %f is avg, %f is sum\n", avg, sum);
    return 0;
}
macbook:Desktop> gcc avg_sum_v2.c 
macbook:Desktop> ./a.out
 6291936479301977399843880960.000000 is avg, 75503235390440487363303964672.000000 is sum
macbook:Desktop> cat avg_sum_v3.c
#include <stdio.h>

void avg_sum (float a[], int n, float *avg, float *sum)
{
    int i;
    // Corrected version 
    // plus printfs to check values
    *sum = 0.0; // *sum = 0.0
    for (i=0;i<n;i++) {
        printf("  %f += %f\n", *sum, a[i]);
        *sum += a[i]; // *sum = *sum + a[i]
    }
    *avg = *sum / n; // *avg= *sum / n
    printf("  avg = %f / %d = %f\n", *sum, n, *avg);
}

int main() {
    float a[] = {3.0, 4.5, 6.7};

    float avg, sum;
    int a_size = sizeof(a);
    printf("a size is %d\n", a_size);

    avg_sum(a, a_size, &avg, &sum);

    // but the results do not make sense.
    printf(" %f is avg, %f is sum\n", avg, sum);
    return 0;
}
macbook:Desktop> gcc avg_sum_v3.c
macbook:Desktop> ./a.out
a size is 12
  0.000000 += 3.000000
  3.000000 += 4.500000
  7.500000 += 6.700000
  14.200000 += 0.000000
  14.200000 += 7858160213300908581191680.000000
  7858160213300908581191680.000000 += -4346457425528750080.000000
  7858155601614890153803776.000000 += 63897547522140047286124675072.000000
  63905405539967542375760265216.000000 += 0.000000
  63905405539967542375760265216.000000 += -0.000000
  63905405539967542375760265216.000000 += 0.000000
  63905405539967542375760265216.000000 += 0.000000
  63905405539967542375760265216.000000 += 0.000000
  avg = 63905405539967542375760265216.000000 / 12 = 5325450461663961864646688768.000000
 5325450461663961864646688768.000000 is avg, 63905405539967542375760265216.000000 is sum
macbook:Desktop> cat avg_sum_v4.c
#include <stdio.h>

void avg_sum (float a[], int n, float *avg, float *sum)
{
    int i;
    // Corrected version 
    // plus printfs to check values
    *sum = 0.0; // *sum = 0.0
    for (i=0;i<n;i++) {
        printf("  %f += %f\n", *sum, a[i]);
        *sum += a[i]; // *sum = *sum + a[i]
    }
    *avg = *sum / n; // *avg= *sum / n
    printf("  avg = %f / %d = %f\n", *sum, n, *avg);
}

int main() {
    float a[] = {3.0, 4.5, 6.7};

    float avg, sum;
    // The problem is with finding the size
    int a_size = sizeof(a);
    int a_size2 = sizeof(a) / sizeof(float);
    printf("a size is %d\n", a_size);
    printf("a size should be %d\n", a_size2);

    avg_sum(a, a_size, &avg, &sum);

    // but the results do not make sense.
    printf(" %f is avg, %f is sum\n", avg, sum);
    return 0;
}
macbook:Desktop> gcc avg_sum_v4.c
macbook:Desktop> ./a.out
a size is 12
a size should be 3
  0.000000 += 3.000000
  3.000000 += 4.500000
  7.500000 += 6.700000
  14.200000 += 0.000000
  14.200000 += -8311412856093016760254464.000000
  -8311412856093016760254464.000000 += -0.000000
  -8311412856093016760254464.000000 += 2352222551033577455055011840.000000
  2343911186023726879478906880.000000 += 0.000000
  2343911186023726879478906880.000000 += -0.000000
  2343911186023726879478906880.000000 += 0.000000
  2343911186023726879478906880.000000 += 0.000000
  2343911186023726879478906880.000000 += 0.000000
  avg = 2343911186023726879478906880.000000 / 12 = 195325932168643906623242240.000000
 195325932168643906623242240.000000 is avg, 2343911186023726879478906880.000000 is sum
macbook:Desktop> cd csc3320_Fall2026/programs/C_ch11
macbook:C_ch11> cat bad_ptr.c
Don't return a ptr to local var

        int *f(void)
        {
            int a;
            ...
            return &a;
        }

Once 'f' returns, the variable 'a' does not exist, so the pointer to it
will be invalid.

macbook:C_ch11> cat const_ex1.c 

        void f(const int *p)
        {
            *p = 0; /*  wrong: p is a pointer
                        to a ``constant integer'' */
        }

macbook:C_ch11> cat dont_do_this.c
#include <stdio.h>

int main() {

  int *p;
  printf("%d\n", *p);

  return 0;
}
macbook:C_ch11> gcc dont_do_this.c
macbook:C_ch11> ./a.out
-134919344
macbook:C_ch11> cat indirection.c
/* 
  indirection -- don't do this without assigning value first
*/
#include <stdio.h>

int main (void) {

  int *p;
  printf("%d", *p);

  printf("\n");

  return 0;
}


macbook:C_ch11> cat maxmin.c
/*********************************************************
 * From C PROGRAMMING: A MODERN APPROACH, Second Edition *
 * By K. N. King                                         *
 * Copyright (c) 2008, 1996 W. W. Norton & Company, Inc. *
 * All rights reserved.                                  *
 * This program may be freely distributed for class use, *
 * provided that this copyright notice is retained.      *
 *********************************************************/

/* maxmin.c (Chapter 11, page 250) */
/* Finds the largest and smallest elements in an array */

#include <stdio.h>

#define N 10

void max_min(int a[], int n, int *max, int *min);

int main(void)
{
  int b[N], i, big, small;

  printf("Enter %d numbers: ", N);
  for (i = 0; i < N; i++)
    scanf("%d", &b[i]);

  max_min(b, N, &big, &small);

  printf("Largest: %d\n", big);
  printf("Smallest: %d\n", small);

  return 0;
}

void max_min(int a[], int n, int *max, int *min)
{
  int i;

  *max = *min = a[0];
  for (i = 1; i < n; i++) {
    if (a[i] > *max)
      *max = a[i];
    else if (a[i] < *min)
      *min = a[i];
  }
}

macbook:C_ch11> gcc maxmin.c
macbook:C_ch11> ./a.out
Enter 10 numbers: 11 12 13 14 15 16 17 18 19 100000
Largest: 100000
Smallest: 11
macbook:C_ch11> ./a.out     
Enter 10 numbers: 100000 12 13 14 15 16 17 18 11 19
Largest: 100000
Smallest: 11
macbook:C_ch11> cat types_of_pointers.c


    int *p;    /* points only to integers */
    char *str; /* points only to characters */
    double *q; /* points only to doubles */
    int i, j, a[10], *p, *q ; /* p and q point to integers */


    int i=2, j, *p; /* p points nowhere */
    p = &i; /* p points to integer variable i */
    j = *p; /* same as j=i */


    int i=2, *p=&i; /* p points to variable i */


    int i, j, *p = &i;
    i = 1;
    printf("i = %d\n", i);
    printf("*p = %d\n", *p);

    *p = 4;

    printf("i = %d\n", i);
    printf("*p = %d\n", *p);

    j = *&i;
    printf("j = %d\n", j);

macbook:C_ch11> cat ptr_assign1.c 
/* 
  ptr_assign1.c
*/
#include <stdio.h>

int main (void) {

  int i=1, j=2, *p, *q;
  p = &i;
  q = p;

  *p = 5;  // (Same as i = 5)

  printf("p points to %d\n", *p);
  printf("q points to %d\n", *q);

  return 0;
}


macbook:C_ch11> gcc ptr_assign1.c 
macbook:C_ch11> ./a.out
p points to 5
q points to 5
macbook:C_ch11> cat pointer2a.c
/* 
  indirection -- don't do this without assigning value first
*/
#include <stdio.h>

int main (void) {

  int a = 3;
  int *p;
  p = &a;

  printf("p = %d\n", *p);
  (*p)++;
  printf("p = %d\n", *p);
  printf("a = %d\n", a);

  printf("\n");

  return 0;
}


macbook:C_ch11> gcc pointer2a.c
macbook:C_ch11> ./a.out
p = 3
p = 4
a = 4

macbook:C_ch11> diff pointer2a.c pointer2a_v2.c 
13c13
<   (*p)++;
---
>   (p++);
macbook:C_ch11> gcc pointer2a_v2.c 
macbook:C_ch11> ./a.out
p = 3
p = 0
a = 3

macbook:C_ch11> cat q12.c
cat: q12.c: No such file or directory
macbook:C_ch11> cat ~/Desktop/q12.c
#include <stdio.h>

int main() {
    // Each number is the sum of the previous two
    int Fibonacci[] = { 0, 1, 1, 2, 3, 5, 8, 13, 21, 34}; 
    int *p;
    p = &Fibonacci[6];
    p = p + 2; 
    printf("%d\n", *p);
    // What value will it print?

    return 0;
}
macbook:C_ch11> gcc ~/Desktop/q12.c
macbook:C_ch11> ./a.out
21
macbook:C_ch11> cp ~/Desktop/q12.c ~/Desktop/q12a.c
macbook:C_ch11> vi ~/Desktop/q12.c
macbook:C_ch11> vi ~/Desktop/q12a.c
macbook:C_ch11> gcc ~/Desktop/q12a.c
macbook:C_ch11> ./a.out
21
macbook:C_ch11> vi ~/Desktop/q12a.c 
macbook:C_ch11> gcc ~/Desktop/q12a.c
macbook:C_ch11> ./a.out             
9
macbook:C_ch11> cat ~/Desktop/q12a.c
#include <stdio.h>

int main() {
    // Each number is the sum of the previous two
    int Fibonacci[] = { 0, 1, 1, 2, 3, 5, 8, 13, 21, 34}; 
    int *p;
    p = &Fibonacci[6];
    //p = p + 2; 
    //(p++);
    //(p)++;
    (*p)++;
    printf("%d\n", *p);
    // What value will it print?

    return 0;
}
macbook:C_ch11> cd ../C_ch12
macbook:C_ch12> cat bad_idea.c
#include <stdio.h>

#define NUM_ROWS 5
#define NUM_COLS 5

int main() {
  int a[NUM_ROWS][NUM_COLS];
  int row, col;
  
  // row should not be = to NUM_ROWS
  for (row = 0; row < NUM_ROWS; row++)
    for (col = 0; col <= NUM_COLS; col++) {
      if (col < NUM_COLS)
        a[row][col] = 0;
    }

  // print 
  for (row = 0; row < NUM_ROWS; row++) {
    for (col = 0; col < NUM_COLS; col++)
      printf("  %d", a[row][col]);
    printf("\n");
  }
 
  return 0;
}
macbook:C_ch12> gcc bad_idea.c
macbook:C_ch12> ./a.out
  0  0  0  0  0
  0  0  0  0  0
  0  0  0  0  0
  0  0  0  0  0
  0  0  0  0  0
macbook:C_ch12> vi bad_idea.c 
macbook:C_ch12> cat bad_idea.c
#include <stdio.h>

#define NUM_ROWS 5
#define NUM_COLS 5

int main() {
  int a[NUM_ROWS][NUM_COLS];
  int row, col;
  
  // row should not be = to NUM_ROWS
  for (row = 0; row < NUM_ROWS; row++)
    for (col = 0; col <= NUM_COLS; col++) {
      //if (col < NUM_COLS)
        a[row][col] = 0;
    }

  // print 
  for (row = 0; row < NUM_ROWS; row++) {
    for (col = 0; col < NUM_COLS; col++)
      printf("  %d", a[row][col]);
    printf("\n");
  }
 
  return 0;
}
macbook:C_ch12> gcc bad_idea.c
macbook:C_ch12> ./a.out       
  0  0  0  0  0
  0  0  0  0  0
  0  0  0  0  0
  0  0  0  0  0
  0  0  0  0  0
zsh: abort      ./a.out
macbook:C_ch12> vi bad_idea.c
macbook:C_ch12> gcc bad_idea.c
macbook:C_ch12> ./a.out       
done
zsh: abort      ./a.out
macbook:C_ch12> cst ch12_1.c 
zsh: command not found: cst
macbook:C_ch12> cat ch12_1.c
#include <stdio.h>

int main(){
        int a[8], *p, *q;
        p = &a[0];
        
        // initialize the array a
        for (int i=0; i<8; i++)
          a[i] = i;

//Add an integer to a pointer

        p = &a[2];      //  When index is out of bound, 
        q = p + 3;      // accessing to *p may generate 
        printf("%d\n", *q);  
        //p += 4;         // unexpected result
        q += 4;         // unexpected result
        //printf("%d\n", *p);
        printf("%d\n", *q);

//Subtract an integer from a pointer

        p = &a[6];
        q = p - 3; 
        printf("%d\n", *q);
        p -= 6;
        printf("%d\n", *p);

        return 0;
}
macbook:C_ch12> echo a = 0 1 2 3 4 5 6 7
a = 0 1 2 3 4 5 6 7
macbook:C_ch12> gcc ch12_1.c 
macbook:C_ch12> ./a.out
5
-2086831260
3
0
macbook:C_ch12> exit

Saving session...
...copying shared history...
...saving history...truncating history files...
...completed.

Script done on Mon Oct 12 18:44:55 2026