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C Programming: A Modern Approach (Second Edition)

Chapter 8

Answers to Selected Exercises

1. [was #4] The problem with sizeof(a) / sizeof(t) is that it can't easily be checked for correctness by someone reading the program. (The reader would have to locate the declaration of a and make sure that its elements have type t.)

2. [was #8] To use a digit d (in character form) as a subscript into the array a, we would write a[d-'0']. This assumes that digits have consecutive codes in the underlying character set, which is true of ASCII and other popular character sets.

7. [was #10] 

const int segments[10][7] = {{1, 1, 1, 1, 1, 1},
                             {0, 1, 1},
                             {1, 1, 0, 1, 1, 0, 1},
                             {1, 1, 1, 1, 0, 0, 1},
                             {0, 1, 1, 0, 0, 1, 1},
                             {1, 0, 1, 1, 0, 1, 1},
                             {1, 0, 1, 1, 1, 1, 1},
                             {1, 1, 1},
                             {1, 1, 1, 1, 1, 1, 1},
                             {1, 1, 1, 1, 0, 1, 1}};

Answers to Selected Programming Projects

2. [was #2] 

#include <stdio.h>

int main(void)
{
  int digit_count[10] = {0};
  int digit;
  long n;

  printf("Enter a number: ");
  scanf("%ld", &n);

  while (n > 0) {
    digit = n % 10;
    digit_count[digit]++;
    n /= 10;
  }

  printf ("Digit:      ");
  for (digit = 0; digit <= 9; digit++)
    printf("%3d", digit);
  printf("\nOccurrences:");
  for (digit = 0; digit <= 9; digit++)
    printf("%3d", digit_count[digit]);
  printf("\n");

  return 0;
}

5. [was #6] 

#include <stdio.h>

#define NUM_RATES ((int) (sizeof(value) / sizeof(value[0])))
#define INITIAL_BALANCE 100.00

int main(void)
{
  int i, low_rate, month, num_years, year;
  double value[5];

  printf("Enter interest rate: ");
  scanf("%d", &low_rate);
  printf("Enter number of years: ");
  scanf("%d", &num_years);

  printf("\nYears");
  for (i = 0; i < NUM_RATES; i++) {
    printf("%6d%%", low_rate + i);
    value[i] = INITIAL_BALANCE;
  }
  printf("\n");

  for (year = 1; year <= num_years; year++) {
    printf("%3d    ", year);
    for (i = 0; i < NUM_RATES; i++) {
      for (month = 1; month <= 12; month++)
        value[i] += ((double) (low_rate + i) / 12) / 100.0 * value[i];
      printf("%7.2f", value[i]);
    }
    printf("\n");
  }

  return 0;
}

8. [was #12] 

#include <stdio.h>

#define NUM_QUIZZES  5
#define NUM_STUDENTS 5

int main(void)
{
  int grades[NUM_STUDENTS][NUM_QUIZZES];
  int high, low, quiz, student, total;

  for (student = 0; student < NUM_STUDENTS; student++) {
    printf("Enter grades for student %d: ", student + 1);
    for (quiz = 0; quiz < NUM_QUIZZES; quiz++)
      scanf("%d", &grades[student][quiz]);
  }

  printf("\nStudent  Total  Average\n");
  for (student = 0; student < NUM_STUDENTS; student++) {
    printf("%4d      ", student + 1);
    total = 0;
    for (quiz = 0; quiz < NUM_QUIZZES; quiz++)
      total += grades[student][quiz];
    printf("%3d     %3d\n", total, total / NUM_QUIZZES);
  }

  printf("\nQuiz  Average  High  Low\n");
  for (quiz = 0; quiz < NUM_QUIZZES; quiz++) {
    printf("%3d     ", quiz + 1);
    total = 0;
    high = 0;
    low = 100;
    for (student = 0; student < NUM_STUDENTS; student++) {
      total += grades[student][quiz];
      if (grades[student][quiz] > high)
        high = grades[student][quiz];
      if (grades[student][quiz] < low)
        low = grades[student][quiz];
    }
    printf("%3d    %3d   %3d\n", total / NUM_STUDENTS, high, low);
  }

  return 0;
}
Copyright © 2008, 1996 W. W. Norton & Company, Inc. All rights reserved.

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