CS 1005, C Term 2000
Introduction to Programming
Solution to the Practice Problems for Test 1

  1. a) Circle all syntactically correct C++ statements among the following.
       int k;    (circled)
       bool IsEven(int n);    (circled)
       k-;  <-- incorrect. Closest match is k--; (decrements k by one)
       if (k==1) {    (circled)
          k += 1;     (circled)

    b) State two advantages of using functions in program design.

       Functions allow one to decompose a complex program into smaller,
       more easily understandable pieces.
       Functions allow code reuse. A function is defined only once,
       but it can be called (used) multiple times in a program.

  2. Using the function IsPrime whose specification is given here:
       bool IsPrime(int n)
       // Returns true if n>1 and the only divisors of n are 1 and n
       // Returns false otherwise
       (function body not shown)
    fill in the main() function below so that it prints all prime numbers between 1 and 10,000 to the console output cout. A prime number is an integer p for which the function invocation IsPrime(n) returns true. Consecutive numbers should be separated by spaces in the output.
       One possibility:
       (important point: there should *not* be any commas in 10000 below)
       int main() {
          for (int i=2; i<=10000; i++) {
             if (IsPrime(i))
                cout << i << " ";
          return 0;
       Another possibility:
       int main() {
          int i=2;
          while (i<=10000) {
             if (IsPrime(i))
                cout << i << " ";
          return 0;

  3. For each of the following program segments, state what output is produced.
    a) int i=12;
       cout << i%5;     output:  2
    b) int j=9;
       cout << ++j;     output:  10
    c) int k=1;
       while (k/4 < 2) 
       cout << k;       output:  9
    d) bool flag=false;
       for (int i=1; i<=1000; i++)
          if (i%3 == 0)
             flag = !flag;
       if (flag)
          cout << "true";     
       else if (!flag)
          cout << "false";     output:  true
    e) int lambda = 32;
       while (lambda > 0) {
          int k=lambda;
          while (k > 0) {
             cout << "*";
             k /= 2;
          cout << endl;
          lambda /= 3;         output:  ******
       }                                ****

  4. Circle all incorrect statements in the following C++ program. In each case, give a brief explanation of what errors are associated with the statement. You may assume that the entirety of the program source file is shown below.
       int main() {
          double x      error: missing final semicolon
          x = 3;        warning, but no error: conversion from int to double 
          y = 4.5;      error: object named y has not been declared
          cout << the value of x+y equals << x+y;  error: missing quotation marks
          return 0.0;   warning, but no error: conversion from double to int 

  5. Examine the function named UFO defined below and state in words what numbers n yield a return value of true when UFO is called with n as its input argument.
       bool UFO(int n)
          while (n%2 == 0)
          return (n==1);
       Answer: UFO(n) returns true if n is a power of 2, and returns false 
       otherwise. For example, UFO(32) returns true because 32 equals 2 to 
       the 5th power, while UFO(7) returns false. By the way, UFO stands 
       for "Unidentified Function Object".