3.4. Exercises#

Many of these exercises are taken from past exams of APS105 Computer Fundamentals courses at University of Toronto. The solutions are provided in the answer boxes.

3.4.1. Conditional Statements#

3.4.1.1. Practice 1#

Question 2 in Winter 2018 Midterm Exam

Write a single C statement — which contains exactly one terminating semi-colon (;), and does not contain brace brackets ({ or }) — that declares a bool variable named isHighlighted, and sets its value to true if and only if the value stored in an integer variable named characterCount is an even positive number. Assume that the variable characterCount has already been declared and initialized.

Answer

bool isHighlighted = characterCount % 2 == 0 && characterCount > 0;

3.4.1.2. Practice 2#

Question 2 in Winter 2019 Midterm Exam

Write a single C statement that declares a boolean-type variable named divisible and assigns true to divisible if and only if the value stored in the int variable named numOfItems is exactly divisible by \(5\) or \(7\). Assume that variable numOfItems has been declared and initialized.

Answer

bool divisible = numOfItems % 5 == 0 || numOfItems % 7 == 0;

3.4.1.3. Practice 3#

Question 7 in Winter 2018 Final Exam

Evaluate the following relational expressions by circling the right answer.

Expression

true / false

'\O' == 0

int x = 10 % 8;
(x > 0) && (x % 2 == 0) && !false

'c' - 3 == 'a'

int w = rand() % 75 * 2 - 99;
(w < -99) || (w > 49);

Answer

Expression

true / false

'\O' == 0

true, since \0 has ASCII code of zero

int x = 10 % 8;
(x > 0) && (x % 2 == 0) && !false

true, since x stores \(2\)

'c' - 3 == 'a'

false, since 'c' - 2 == 'a'

int w = rand() % 75 * 2 - 99;
(w < -99) || (w > 49);

false, since the range of random numbers in w is between -99 and 49 inclusive

3.4.1.4. Practice 4#

Question 3 in Winter 2022 Midterm Exam

Suppose that x and y are int type variables, write a single C statement that is equivalent to the following statement, but is simpler, i.e. with fewer boolean and relational operators.

bool var = !(x <= y && y <= z);

Answer

bool var = (x > y || y > z);

3.4.2. Nested-if Statements#

3.4.2.1. Practice 1#

Modified version of Question 7 in Winter 2019 Midterm Exam

Write C program to find the median, which is the number at the middle, among three integers p, q and r. The program should prompt the user to enter three integers, which get stored in p, q and r. Your program should print the value of the number at the middle. For example, with integers \(2\), \(7\), and \(5\) as input, the function returns 5; with integers \(6\), \(4\), and \(6\) as input, the function returns \(6\).

Answer

Download median.c to get the following code.

#include <stdio.h>
int main(void) {
  int p = 0, q = 0, r = 0;
  printf("Enter three integers: ");
  scanf("%d %d %d", &p, &q, &r);

  if ((p >= q && p <= r) || (p >= r && p <= q)) {
    printf("%d", p);
  } else if ((q >= p && q <= r) || (q >= r && q <= p)) {
    printf("%d", q);
  } else {
    printf("%d", r);
  }
}

3.4.2.2. Practice 2#

Modified Version of Question 4 in Winter 2022 Midterm Exam

The following program finds the middle character, e.g., if we have a = 'a', b = 'b', and c = 'c', the program prints b. Rewrite this function such that it only uses one printf and one nested if-else statement.

int main(void) {
  char a = '\0', b = '\0', c = '\0';
  printf("Enter three characters: ");
  scanf("%c %c %c", &a, &b, &c);
  if (a < b) {
    if (b < c) {
      printf("%c", b);
    } else if (a < c) {
      printf("%c", c);
    } else {
      printf("%c", a);
    }
  }

  if (c < b) {
    printf("%c", b);
  }
  if (a < c) {
    printf("%c", a);
  }
  printf("%c", c);
}

Answer

int main(void) {
  char a = '\0', b = '\0', c = '\0', result = '\0';
  printf("Enter three characters: ");
  scanf("%c %c %c", &a, &b, &c);

  char result = a;

  if ((a < b && b < c) || (c < b && b < a)) {
    result = b;
  } else if ((a < c && c < b) || (b < c && c < a)) {
    result = c;
  }

  printf("%c", result);
}