C语言程序设计_现代方法

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Answers to Selected Exercises and Programming Projects The following links lead to answers to selected exercises and programming projects from the second edition of C Programming: A Modern Approach. Exercises and projects for which answers are provided are marked with a icon in the book. Note: These exercises and projects were originally the even-numbered exercises in the first edition. (The first edition did not distinguish between exercises and programming projects.) For the benefit of readers who have the first edition, the original exercise number is given in square brackets. For example, the notation [was #4] indicates that the number of the exercise (or programming project) was 4 in the first edition. If an answer is different because of second-edition changes, the word "modified" will appear inside the brackets: [was #4; modified]. Please email me with comments and error reports. Chapter 2 Answers to Selected Exercises 2. [was #2] (a) The program contains one directive (#include) and four statements (three calls of printf and one return). (b) Parkinson's Law: Work expands so as to fill the time available for its completion. 3. [was #4] #include int main(void)

{ int height = 8, length = 12, width = 10, volume; volume = height * length * width; printf("Dimensions: %dx%dx%d\n", length, width, height); printf("Volume (cubic inches): %d\n", volume); printf("Dimensional weight (pounds): %d\n", (volume + 165) / 166); return 0; } 4. [was #6] Here's one possible program: #include int main(void) { int i, j, k; float x, y, z; printf("Value of i: %d\n", i); printf("Value of j: %d\n", j); printf("Value of k: %d\n", k); printf("Value of x: %g\n", x); printf("Value of y: %g\n", y); printf("Value of z: %g\n", z); return 0; } When compiled using GCC and then executed, this program produced the following output: Value of i: 5618848 Value of j: 0 Value of k: 6844404 Value of x: 3.98979e-34 Value of y: 9.59105e-39 Value of z: 9.59105e-39 The values printed depend on many factors, so the chance that you'll get exactly these numbers is small. 5. [was #10] (a) is not legal because 100_bottles begins with a digit. 8. [was #12] There are 14 tokens: a, =, (, 3, *, q, -, p, *, p, ), /, 3, and ;.

Answers to Selected Programming Projects 4. [was #8; modified] #include int main(void) { float original_amount, amount_with_tax; printf("Enter an amount: "); scanf("%f", &original_amount); amount_with_tax = original_amount * 1.05f; printf("With tax added: $%.2f\n", amount_with_tax); return 0; } The amount_with_tax variable is unnecessary. If we remove it, the program is slightly shorter: #include int main(void) { float original_amount; printf("Enter an amount: "); scanf("%f", &original_amount); printf("With tax added: $%.2f\n", original_amount * 1.05f); return 0; } Copyright © 2008, 1996 W. W. Norton & Company, Inc. All rights reserved. Chapter 3 Answers to Selected Exercises 2. [was #2] (a) printf("%-8.1e", x); (b) printf("%10.6e", x); (c) printf("%-8.3f", x);

(d) printf("%6.0f", x); 5. [was #8] The values of x, i, and y will be 12.3, 45, and .6, respectively. Answers to Selected Programming Projects 1. [was #4; modified] #include int main(void) { int month, day, year; printf("Enter a date (mm/dd/yyyy): "); scanf("%d/%d/%d", &month, &day, &year); printf("You entered the date %d%.2d%.2d\n", year, month, day); return 0; } 3. [was #6; modified] #include int main(void) { int prefix, group, publisher, item, check_digit; printf("Enter ISBN: "); scanf("%d-%d-%d-%d-%d", &prefix, &group, &publisher, &item, &check_digit); printf("GS1 prefix: %d\n", prefix); printf("Group identifier: %d\n", group); printf("Publisher code: %d\n", publisher); printf("Item number: %d\n", item); printf("Check digit: %d\n", check_digit); /* The five printf calls can be combined as follows: printf("GS1 prefix: %d\nGroup identifier: %d\nPublisher code: %d\nItem number: %d\nCheck digit: %d\n", prefix, group, publisher, item, check_digit); */ return 0; }

Copyright © 2008, 1996 W. W. Norton & Company, Inc. All rights reserved. Chapter 4 Answers to Selected Exercises 2. [was #2] Not in C89. Suppose that i is 9 and j is 7. The value of (-i)/j could be either –1 or –2, depending on the implementation. On the other hand, the value of -(i/j) is always –1, regardless of the implementation. In C99, on the other hand, the value of (-i)/j must be equal to the value of -(i/j). 9. [was #6] (a) 63 8 (b) 3 2 1 (c) 2 -1 3 (d) 0 0 0 13. [was #8] The expression ++i is equivalent to (i += 1). The value of both expressions is i after the increment has been performed. Answers to Selected Programming Projects 2. [was #4] #include int main(void) { int n; printf("Enter a three-digit number: "); scanf("%d", &n); printf("The reversal is: %d%d%d\n", n % 10, (n / 10) % 10, n / 100); return 0; } Copyright © 2008, 1996 W. W. Norton & Company, Inc. All rights reserved.

Chapter 5 Answers to Selected Exercises 2. [was #2] (a) 1 (b) 1 (c) 1 (d) 1 4. [was #4] (i > j) - (i < j) 6. [was #12] Yes, the statement is legal. When n is equal to 5, it does nothing, since 5 is not equal to –9. 10. [was #16] The output is onetwo since there are no break statements after the cases. Answers to Selected Programming Projects 2. [was #6] #include int main(void) { int hours, minutes; printf("Enter a 24-hour time: "); scanf("%d:%d", &hours, &minutes); printf("Equivalent 12-hour time: "); if (hours == 0) printf("12:%.2d AM\n", minutes); else if (hours < 12) printf("%d:%.2d AM\n", hours, minutes); else if (hours == 12) printf("%d:%.2d PM\n", hours, minutes); else printf("%d:%.2d PM\n", hours - 12, minutes); return 0; } 4. [was #8; modified] #include

int main(void) { int speed; printf("Enter a wind speed in knots: "); scanf("%d", &speed); if (speed < 1) printf("Calm\n"); else if (speed <= 3) printf("Light air\n"); else if (speed <= 27) printf("Breeze\n"); else if (speed <= 47) printf("Gale\n"); else if (speed <= 63) printf("Storm\n"); else printf("Hurricane\n"); return 0; } 6. [was #10] #include int main(void) { int check_digit, d, i1, i2, i3, i4, i5, j1, j2, j3, j4, j5, first_sum, second_sum, total; printf("Enter the first (single) digit: "); scanf("%1d", &d); printf("Enter first group of five digits: "); scanf("%1d%1d%1d%1d%1d", &i1, &i2, &i3, &i4, &i5); printf("Enter second group of five digits: "); scanf("%1d%1d%1d%1d%1d", &j1, &j2, &j3, &j4, &j5); printf("Enter the last (single) digit: "); scanf("%1d", &check_digit); first_sum = d + i2 + i4 + j1 + j3 + j5; second_sum = i1 + i3 + i5 + j2 + j4; total = 3 * first_sum + second_sum; if (check_digit == 9 - ((total - 1) % 10)) printf("VALID\n"); else printf("NOT VALID\n");

return 0; } 10. [was #14] #include int main(void) { int grade; printf("Enter numerical grade: "); scanf("%d", &grade); if (grade < 0 || grade > 100) { printf("Illegal grade\n"); return 0; } switch (grade / 10) { case 10: case 9: printf("Letter grade: A\n"); break; case 8: printf("Letter grade: B\n"); break; case 7: printf("Letter grade: C\n"); break; case 6: printf("Letter grade: D\n"); break; case 5: case 4: case 3: case 2: case 1: case 0: printf("Letter grade: F\n"); break; } return 0; } Copyright © 2008, 1996 W. W. Norton & Company, Inc. All rights reserved.

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