Formatted Input/Output

Exercises

Question 3.1

What output do the following calls of printf produce?

1. printf("%6d,%4d", 86, 1040);
2. printf ("%12.5e", 30.253);
3. printf("%.4f", 83.162);
4. printf("%-6.2g",.0000009979);

Output

    86,1040
 3.02530e+01
83.1620
1e-06

Program

#include <stdio.h>

int main (void) {
  printf("%6d,%4d\n", 86, 1040);
  printf("%12.5e\n", 30.253);
  printf("%.4f\n", 83.162);
  printf("%-6.2g\n", .0000009979);

  return 0;

Login to view full code

---

Question 3.2

Write calls of printf that display a float variable x in the following formats.

1. Exponential notation; left-justified in a field of size 8; one digit after the decimal point.
2. Exponential notation; right-justified in a field of size 10; six digits after the decimal point.
3. Fixed decimal notation: left-justified in a field of size 8; three digits after the decimal point.
4. Fixed decimal notation; right-justified in a field of size 6: no digits after the decimal point.

Output

7.9e+02
7.891235e+02
789.123
   789

Program

#include <stdio.h>

int main (void) {
  float x = 789.123456;

  printf("%-8.1e\n", x);
  printf("%10.6e\n", x); 
  printf("%-8.3f\n", x);
  printf("%6.0f\n", x);

Login to view full code

---

Question 3.3

For each of the following pairs of scanf format strings, indicate whether or not the two strings are equivalent. If they're not. show how they can be distinguished.

1. "%d" versus " %d"
2. "%d-%d-%d" versus "%d -%d -%d"
3. "%f" versus "%f "
4. "%f,%f" versus "%f, %f"

Answer

(a) "%d"       versus " %d"          → No difference
(b) "%d-%d-%d" versus "%d -%d -%d"   → Difference
(c) "%f"       versus "%f "          → Difference (expects a white space character)
(d) "%f,%f"    versus "%f, %f"       → No difference

When it comes to different types of formats:

1. "%d" expects for an integer that can be a number, a sign (plus or minus). " %d" does not really have that difference with the former expression.
2. "%d-%d-%d" expects a number of format "<num>-<num>-<num>", so when we enter a number like "123 -567 -894", there can be problems. scanf first checks for the number "123" and sees it matches the pattern but when it encounters the whitespace character, it cannot do anything so it puts it back for the next scanf to check.
3. "%f" expects a number, a sign (plus or minus) and decimal point or e (exponent). "%f " expects the same as the former pattern but it also expects a whitespace character so unless "\n" or "\t" or any other character is entered, it does not complete the input operation.
4. "%f,%f" expects a floating point number, a comma and another floating point number. Similar to the pattern in part a, the latter one "%f, %f" expects the same without having any issue.

---

Question 3.4

Suppose that we call scanf as follows:
scanf("%d%f%d", &i, &x, &j) ;
If the user enters
10.3 5 6
what will be the values of i, x, and j after the call? (Assume that i and j are int variables and x is a float variable.)

Answer

Since the pattern scanf is looking for is int, then float and finally another int and when we enter the given values, the following may happen:
scanf encounters 10 followed by a . which is not used to describe an integer, so it is put back and 10 is stored in i. .3 is checked and since a whitespace is encountered, it stops to store .3 in x. Finally, 5 and a whitespace is encountered, so 5 is stored in j.

i = 10, x = 0.3, j = 5

---

Question 3.5

Suppose that we call scanf as follows:
scanf("%f%d%f", &x, &i, &y) ;
If the user enters
12.3 45.6 789
what will be the values of x, i, and y after the call? (Assume that x and y are float variables and i is an int variable.)

Answer

Similar to the process described in Exercise 4, the following values will be stored:

x = 12.3, i = 45, y = 0.6

---

Question 3.6

Show how to modify the addfrac.c program of Section 3.2 so that the user is allowed to enter fractions that contain spaces before and after each / character.

/* Adds two fractions */

#include <stdio.h>

int main(void)
{
   int num1, denom1, num2, denom2, result_num, result_denom;

   printf("Enter first fraction: ");
   scanf("%d/%d", &num1, &denom1);

   printf("Enter second fraction: ");
   scanf("%d/%d", &num2, &denom2);

   result_num = num1 * denom2 + num2 * denom1;
   result_denom = denoml * denom2;
   printf("The sum is %d/%d\n", result_num, result_denom);

   return 0;
}

Program

#include <stdio.h>

int main (void) {
  int num1 = 0, num2 = 0;
  int denom1 = 1, denom2 = 1;
  int result_num = 0, result_denom = 1;

  printf("Enter the first fraction: ");
  scanf("%d /%d", &num1, &denom1);

Login to view full code

Programming Projects

Project 3.1

Write a program that accepts a date from the user in the form mm/dd/yyyy and then displays it in the form yyyymmdd:
Enter a date (mm/dd/yyyy): 2/17/2011
You entered the date 20110217

Program

#include <stdio.h>

int main (void) {
  int month = 0, date = 0, year = 0;

  printf("Enter a date (mm/dd/yyyy): ");
  scanf("%d/%d/%d", &month, &date, &year);

  printf("You entered the date %4d%2.2d%2.2d\n", year, month, date);

Login to view full code

---

Project 3.2

Write a program that formats product information entered by the user. A session with the program should look like this:
Enter item number: 583
Enter unit price: 13.5
Enter purchase date (mm/dd/yyyy): 10/24/2010

Item            Unit            Purchase
                Price           Date    
583             $   13.50       10/24/2010

The item number and date should be left justified; the unit price should be right justified. Allow dollar amounts up to $9999.99. Hint: Use tabs to line up the columns.

Program

#include <stdio.h>

int main (void) {
  int item_number, date, month, year;
  float unit_price;

  printf("Enter item number: ");
  scanf("%d", &item_number);
  printf("Enter unit price: ");

Login to view full code

---

Project 3.3

Books are identified by an International Standard Book Number (ISBN). ISBNs assigned after January I. 2007 contain 13 digits, arranged in five groups, such as 978-0-393-97950-3. (Older ISBNs use 10 digits.) The first group (the GSI prefix) is currently either 978 or 979. The group identifier specifies the language or country of origin (for example. 0 and 1 are used in English-speaking countries). The publisher code identifies the publisher (393 is the code for W. W. Norton). The item number is assigned by the publisher to identify a specific book (97950 is the code for this book). An ISBN ends with a check digit that's used to verify the accuracy of the preceding digits. Write a program that breaks down an ISBN entered by the user:
Enter ISBN: 978-0-393-97950-3
GSI prefix: 978
Group identifier: 0
Publisher code: 393
Item number: 97950
Check digit:3

Note: The number of digits in each group may vary: you can't assume that groups have the lengths shown in this example. Test your program with actual ISBN values (usually found on the back cover of a book and on the copyright page).

Program

#include <stdio.h>

int main (void) {
  int gsi_prefix, group_identifier, publisher_code, item_number, check_digits;

  printf("Enter ISBN: ");
  scanf("%d-%d-%d-%d-%d", &gsi_prefix, &group_identifier, &publisher_code, &item_number, &check_digits);

  printf("GSI prefix:         %d\n", gsi_prefix);

Login to view full code

---

Project 3.4

Write a program that prompts the user to enter a telephone number in the form (xxx) xxx-xxxx and then displays the number in the form xxx.xxx.xxx:
Enter phone number [(xxx) xxx-xxxx]: (404) 817-6900
You entered 404.817.6900

Program

#include <stdio.h>

int main (void) {
  int code, first_place, second_place;

  printf("Enter phone number [(xxx) xxx-xxxx]: ");
  scanf("(%d) %d-%d", &code, &first_place, &second_place);

  printf("You entered %d.%d.%d", code, first_place, second_place);

Login to view full code

---

Project 3.5

Write a program that asks the user to enter the numbers from 1 to 16 (in any order) and then displays the numbers in a 4 by 4 arrangement, followed by the sums of the rows, columns, and diagonals:
Enter the numbers from 1 to 16 in any order: 16 3 2 13 5 10 11 8 9 6 7 12 4 15 14 1

16  3  2 13
 5 10 11  8
 9  6  7 12
 4 15 14  1

Row sums: 34 34 34 34
Column sums: 34 34 34 34
Diagonal sums: 34 34

If the row, column, and diagonal sums are all the same (as they are in this example), the numbers are said to form a magic square. The magic square shown here appears in a 1514 engraving by artist and mathematician Albrecht Dürer. (Note that the middle numbers in the last row give the date of the engraving.)

Program

#include <stdio.h>

int main (void) {
  int num_1, num_2, num_3, num_4, num_5, num_6, num_7, num_8, num_9, num_10;
  int num_11, num_12, num_13, num_14, num_15, num_16;
  // int row_sum_1, row_sum_2, row_sum_3, row_sum_4;
  // int col_sum_1, col_sum_2, col_sum_3, col_sum_4;
  // int diag_sum_1, diag_sum_2;

Login to view full code

---

Project 3.6

Modify the addfrac.c program of Section 3.2 so that the user enters both fractions at the same time, separated by a plus sign: Enter two fractions separated by a plus sign: 5/6+3/4
The sum is 38/24

/* Adds two fractions */

#include <stdio.h>

int main(void)
{
   int num1, denom1, num2, denom2, result_num, result_denom;

   printf("Enter first fraction: ");
   scanf("%d/%d", &num1, &denom1);

   printf("Enter second fraction: ");
   scanf("%d/%d", &num2, &denom2);

   result_num = num1 * denom2 + num2 * denom1;
   result_denom = denoml * denom2;
   printf("The sum is %d/%d\n", result_num, result_denom);

   return 0;
}

Program

#include <stdio.h>

int main (void) {
  int num_1, num_2;
  int denom_1, denom_2;
  // int result_num, result_denom;

  printf("Enter two fractions separated by a plus sign: ");
  scanf("%d/%d+%d/%d", &num_1, &denom_1, &num_2, &denom_2);

Login to view full code