3.1. Exercises

Many of these exercises are taken from past exams of ECE 244 Programming Fundamentals courses at University of Toronto. The solutions are provided in the answer boxes.

Headings in this page classify the exercises into different categories: [Easy], [Intermediate], and [Challenging]. I suggest you start by easy exercises and work your way up to the challenging ones.

Question 5 in Fall 2022 Midterm Exam [Easy]

Consider the following program.

#include <fstream>
#include <iostream>
using namespace std;

int main() {
  int a;
  ifstream inFile;
  inFile.open("input.txt");
  if (inFile.fail()) {
    return 1;
  }
  while (1) {
    inFile >> a;
    if (inFile.fail()) {
      cout << "failed.." << endl;
      inFile.clear();
      inFile.ignore(100, '\n');
      continue;
    }
    cout << "a = " << a << endl;
    break;
  }
  return 0;
}

Given the following contents of "input.txt", write the output.

1. "input.txt"

     1
     2
     3
    

   Answer

   a = 1
   

2. "input.txt"

    a32
    b86
    3
    

   Answer

   failed..
   failed..
   a = 3
   

3. "input.txt"

    a32
    b86 3
    

   Answer

   failed..
   failed..
   failed..
   And it keeps repeating
   

Now you remove the infile.clear() from the code, so the program becomes:

#include <fstream>
#include <iostream>
using namespace std;
int main() {
  int a;
  ifstream inFile;
  inFile.open("input.txt");
  if (inFile.fail()) {
    return 1;
  }
  while (1) {
    inFile >> a;
    if (inFile.fail()) {
      cout << "failed.." << endl;
      // inFile.clear(); COMMENTED OUT
      inFile.ignore(100, '\n');
      continue;
    }
    cout << "a = " << a << endl;
    break;
  }
  return 0;
}

1. "input.txt"

    1
    2
    3
    

   Answer

   a = 1
   

2. "input.txt"

    a32
    b86
    3
    

   Answer

   failed..
   failed..
   failed..
   And it keeps repeating
   

3. "input.txt"

    a32
    b86 3
    

   Answer

   failed..
   failed..
   failed..
   And it keeps repeating
   

Question 2 in Fall 2021 Final Exam [Intermediate]

Write a C++ function void readInts() that repeatedly reads integers from the standard input (using cin) and then immediately outputs the input integer (using cout), one integer per line. When a '.' character is encountered, the function prints the message Done on a line by itself and returns. If the user enters any characters other than integer digits or the '.', the function prints the message Error on a line by itself and returns. You may assume the user will never enter eof.

Thus, for example, if the user enters 51 16 700 ., the function prints:

51
16
700
Done

However, if the user enters 101 21 13 abc 444, the function prints:

101
21
13
Error

void readInts() {

Answer

void readInts() {
  int num = 0;
  string dot;
  cin >> num;
  while (!cin.fail()) {  // received a number
    cout << num << endl;
    cin >> num;
  }
  // then read a non-integer number
  string c;
  // need to clear fail flag before doing cin
  cin.clear();
  // Read in a string
  cin >> c;
  if (c == ".") {
    cout << "Done" << endl;
  } else {
    cout << "Error" << endl;
  }
}

Question 3 in Fall 2018 Midterm Exam [Intermediate]

Consider the following program that uses stringstreams to read a command. The command has the following format:

count intArg

The command word is count and intArg is an integer argument. The command must have only one integer argument, e.g count 3.

The function handle_count performs the reading of the integer value. If the integer is valid, it returns true and updates the value of intArg. Otherwise, it returns false.

#include <iostream>
using namespace std;
#include <sstream>
#include <string>
// function prototype
bool handle_count( <fill in the blank> );

int main() {
  string line;
  string command;
  int intArg;
  getline(cin, line);
  stringstream lineStream(line);
  lineStream >> command;
  if (command == "count") {
    if (handle_count( <fill in the blank> )) {
      cout << "Integer argument is " << intArg << endl;
      return (0);
    } else {
      cout << "Invalid arguments" << endl;
      return (-1);
    }
  } else {
    cout << "Invalid command" << endl;
    return (-1);
  }
}

1. Determine the number of arguments and the type of each argument and indicate them in the code above in the prototype of the function, handle_count. Further, indicate what parameters are passed to the function when it is invoked. Write your answers where indicated in the code above.

   You may not modify main by adding or removing line, other than by indicating the formal arguments in the function prototype and actual arguments of the function invocation.

   Answer

   #include <iostream>
   using namespace std;
   #include <sstream>
   #include <string>
   // function prototype
   bool handle_count(stringstream&, int&);
   
   int main() {
     string line;
     string command;
     int intArg;
     getline(cin, line);
     stringstream lineStream(line);
     lineStream >> command;
     if (command == "count") {
       if (handle_count(lineStream, intArg)) {
         cout << "Integer argument is " << intArg << endl;
         return (0);
       } else {
         cout << "Invalid arguments" << endl;
         return (-1);
       }
     } else {
       cout << "Invalid command" << endl;
       return (-1);
     }
   }
   

2. Write the header and body of the handle_count function below so it performs as indicated above.

   Answer

   bool handle_count(stringstream& line, int& intArg) {
     line >> intArg;
     if (line.fail()) {
       return false;
     } 
     string dummy;
     line >> dummy; 
     if (line.fail()) {
       return true;
     } else {
       return false;
     }
   }
   

Question 6 in Fall 2019 Midterm Exam [Intermediate]

For each of the following main functions, indicate the output produced in response to the user entering 1 2 3 4 five on the keyboard followed by the Enter key. Choose only one answer.

#include <iostream>
using namespace std;
int main() {
  int num = 0;
  int sum = 0;
  while (!cin.fail()) {
    cin >> num;
    sum = sum + num;
  }
  cout << sum << endl;
  return (0);
}

Choose one the following choices:

1. 6

2. 10

3. 14

4. None; the program runs in an infinite loop

Answer

3. 14 The last loop when five is entered, num is unchanged and 4 will be added to sum again.

However, in some compilers, sum may be printed to be 10, as the complier will set num to 0 when cin.fail() is raised. This means, 2. 10 is considered correct too.

#include <iostream>
using namespace std;
int main() {
  int num = 0;
  int sum = 0;
  bool more = true;
  while (more) {
    cin >> num;
    if (cin.fail())
      more = false;
    else
      sum = sum + num;
  }
  cout << sum << endl;
  return (0);
}

Choose one the following choices:

1. 6

2. 10

3. 14

4. None; the program runs in an infinite loop

Answer

2. 10

Question 7 in Fall 2019 Midterm Exam [Intermediate]

Write a C++ function void readInts() that repeatedly reads integers from the standard input (using cin) and then immediately outputs the input integer (using cout), one integer per line.

When the end-of-file is reached, the function prints the message "End of File Reached" on a line by itself before returning. If a non-integer is input the function should print the message "Invalid Input" on a line by itself, should discard the rest of the stream and should continue reading integers again until the end-of-file is reached.

void readInts() {

Answer

void readInts() {
  int num = 0;
  cin >> num;
  while (!cin.eof()) {  // received a number
    if (cin.fail()) {
      cin.clear();
      cin.ignore(1000, '\n');
      cout << "Invalid Input" << endl;
      cin >> num;
    } else {
      cout << num << endl;
      cin >> num;
    }
  }
  cout << "End of File Reached" << endl;
}