1. a) What #include statement do you put at the top of a program that does uses cin, cout or endl?

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1 Exercises with solutions. 1. a) What #include statement do you put at the top of a program that does uses cin, cout or endl? #include <iostream> b) What using statement do you always put at the top of your programs (to get standard naming conventions)? using namespace std; c) Declare an integer variable N and initialize it to 10. Any of these: i) int N = 10; ii) int N(10); iii) int N; N = 10; d) Give a statement to increase the value of variable N by 10. Any of these: i) N = N + 10; ii) N += 10; e) What library would you include if you wanted to use the sin, cos, and tan functions? <cmath> f) What library would you include if you wanted to use pseudo-random numbers? <cstdlib> 2. Complete the code segment below to print There are XXX days. if integer x has a value 1 through 7 inclusive. Replace XXX with the value of variable x; note the period. int x; cin >> x; // add your code here if ((x >=1) && (x <= 7)) { cout << There are " << x << " days.\n"; 3. What is the final value of each expression? Watch for integer division. a) / b) 15 / c) (int) / 4; // casting has precedence over division 7 4. You have an integer variable x that holds a four-digit positive integer. Write C++ code to store the middle two digits in integer variable y. Any of these: i) y = x / 10 % 100; ii) y = x % 1000 / 10; 5. What is the output from each code segment below? a) int x = 1, y = 0;

2 if (x > 0 && y < 0) { x = y = 23; cout << x << " " << y << endl; Ans: 1 0 b) int x = 1, y = 0; if (x > 0 y < 0) { x = y = 23; cout << x << " " << y << endl; Ans: c) x = 10; y = 40; if (x >= 10) { if (y < 40) { y++; else { y--; cout << x << " " << y << endl; Ans: d) x = 10; y = 40; if (x >= 10) { if (y < 40) { y++; else { y--; cout << x << " " << y << endl; Ans: e) In part d) above, under what condition(s) would y be incremented? Ans: If x is greater than or equal to 10 and y is less than How many times does each loop execute? a) for (i = 0; i <= 100; i++) { statements; Ans: 101 times b) for (i = 1; i < 100; i++) { statements; Ans: 99 times 7. Examine the code below. What (not how) does the following function do? int mystery(int x, int y, int z) { int temp; // ultimately, holds returned value temp = x; // assume the largest is x if(y > temp) { temp = y; if(z > temp) { temp = z; return temp; Ans: It returns the maximum of x, y, and z.

3 8. The Fibonacci numbers are defined: fibonacci (0) = 1 fibonacci (1) = 1 fibonacci (n) = fibonacci (n 1) + fibonacci (n 2); Write a recursive C++ function to compute the Fibonacci numbers: Ans: int fibonacci (int n) { // fill in if ((n == 0) (n == 1)) { return 1; 9. What is printed in each case: a) cout << 3 * 4+5 << endl; Ans: 17 else { return fibonacci(n-1) + fibonacci(n-2); b) cout << / 4 << endl; Ans: 19 c) string N = "17"; cout << N + "10 / 4" << endl; Ans: 1710 / 4 d) int N = 17; cout << (N = 16) << endl; Ans: Suppose that every time currenttime() is called, it returns the current time in the form of an integer (typically the number of seconds since a certain day in 1970). Using currenttime() and motors(), write C++ code to make the robot move forward at half speed for 45 seconds. Ans: int start = currenttime(); while ((currenttime() - start < 45) { robot.motors(0.5,0.5); 11. If A and B are boolean variables, then the expression (!A) (!B) is equivalent to which of the following conditions: a) (! (A && B)) b) (! (A B))

4 c) (!A) && (!B) d) true Ans: (a) 12. Study the following code segment. int N = 7; int i, x; for (i = 1; i <= N; i++) { cin >> x; if(i % 3 == 0) { cout << endl; cout << endl; cout << i << ". " << x << " "; a) What is displayed with the given input? Watch the endl characters. Input: Ans: b) In terms of N, what is the value of the loop control variable upon termination? Ans: N a) Rewrite the following C++ statement to make it more robust (less prone to error). if (x / y!= 0 && y!= 0) { cout << x / y << endl; Ans: The operands of && are evaluated in order (not mentioned -5 of 6- previously, but now you know!), and we don't want to divide by 0, so: if (y!= 0 && x / y!= 0) { cout << x / y << endl; b) Rewrite the following C++ code segment to make it more efficient and to remove any unnecessary code. if (x < y && y > x) { cout << "Not good.\n"; Ans: "x < y" and "y > x" always have the same truth value, so: if (x < y) { cout << "Not good.\n"; c) Rewrite the following C++ code segment to make it more efficient and to remove any unnecessary code. if (x < y && y >= x) { cout << "Not good.\n"; Ans: Since x<y implies x<=y, which is equivalent to y>=x:

5 if (x < y) { cout << "Not good.\n"; d) Rewrite the following C++ code segment to make it more efficient and to remove any unnecessary code. if (x < y y >= x) { cout << "Not good.\n"; Ans: Similar explanation to previous. if (y >= x) { cout << "Not good.\n"; 14. Give 3 reasons why it's important to comment your code. What are the 2 different ways to comment code in C++ and how are they different? It's important to comment your code because:- 1. it makes easier for other people to understand your program. 2. it helps you while programming to organize and write your code. 3. it helps you track down and debug errors. The // comment style comments out any text on that line to the right of the slashes. The /* */ comment style comments out all code contained between the asterisks. 15. Write the output of the following segments of code. a.) int x = 3; cout << x << 2*x; Ans: 36 b.) cout << "\"Hello\\\n Gandalf!"; Ans: "Hello\ Gandalf! (Note the space before Gandalf.) c.) int x = 7; int y = 3; cout << x/y << " and " << x%y; Ans: 2 and Briefly explain and correct the error(s) in each of the code segments below. a.) string word; cout << "Enter a word: "; cin << word;

6 Ans: The input pull << goes the wrong way. Should be: cin >> word; b.) cout << "Two plus two is " 2+2; Ans: Should be another output push << cout << "Two plus two is " << 2+2; c.) if ( x = 1 ); cout << x; Ans: The = sign is an assignment, not a comparison. After the condition, there should not be a semicolon. if ( x == 1) d.) if ( x = 1 or 2 ) cout << x; Ans: Again uses = sign. Also need to use for "or" and 2 boolean statements: if ( x == 1 x == 2 ) e.) //This code is supposed to compute 10! int N = 10; int factorial = 1; while ( N >= 1 ) { factorial = factorial * N; N--; cout << "10! is " << factorial << ".\n"; Ans: Correctly computes 10!, but the final output statement should occur outside the loop. Otherwise, it prints out 10 different answers for 10! N--; cout << "10! is " << factorial << ".\n"; 17. The program below is supposed to compute the average of two numbers. The program compiles without error, but does not correctly compute the average. Describe the logic error(s) and write the corrected lines. You do not need to rewrite the entire program. The line numbers are written along the left column to help you write your answer; they are not part of the program code. Make as few changes as possible. 1 # include <iostream> 2 using namespace std; 3 int main ( ) {

7 4 int total; 5 cout << "Enter a number: "; 6 int a; 7 cin >> a; 8 total = total + a; 9 cout << "Enter another number: "; 10 int b; 11 cin >> b; 12 total = total + a; 13 double average = total / 2; 14 cout << "The average is " << average << ".\n"; 15 return 0; 16 Ans: Line 8: Adds a to total before total is initialized. Should be: total = a; Line 12: Again adds a to the total. Should have added b, or else total = 2*a. total = total + b; Line 13: Performs integer division, so we will lose fractional part. If the sum is odd, then the average should end.5. We can correct this by casting the variables. double average = (double) total / 2; 18. Write a program (starting from #include) that repeatedly collects positive integers from the user, stopping when the user enters a negative number or zero. After that, output the product of all positive entries. A sample run should appear on the screen like the text below. Enter a number: 3 Enter a number: 10 Enter a number: 2 Enter a number: -213 The product of all your positive numbers is 60. # include <iostream> using namespace std; int main ( ) {

8 int x = 1; int product = 1; while ( x > 0 ) { product *= x; cout << "Enter a number: "; cin >> x; cout << "The product of all your positive numbers is " << product << ".\n"; return 0; Note: This code assumes the user entered at least one positive number, which is a reasonable assumption. We could add an if statement at the beginning to handle the case when the first number entered is non-positive. But the solution above would receive full credit. 19. What does the following code print out? a.) int x = 4; do { cout << x << "+"; x = x+3; while (x%4!= 0); Ans: b.) for (int i=10; i > 5; i--) { if ( i %2 == 0) cout << 2*i << "a"; else cout << i << "b"; Ans: 20a9b16a7b12a c.) string first_name = "Frodo"; string last_name = "Baggins"; if (!(first_name=="frodo" && last_name=="smith")) cout << "true";

9 else cout << "false"; Ans: true 20. Rewrite the following do loop as a for loop. What does it print out? int x = -10; do { cout << x << " & "; x += 2; while (x < 100); Ans: for (int x = -10; x < 100; x +=2) { cout << x << " & "; Prints out the even numbers -10 through 98 with an & in between. 21. What is the output of the following program? Track the variables in a walkthrough table. int my_fun (int a, int& b, int c) { a = 2*a+b; b = c; cout << "In my_fun, a=" << a << " b=" << b << ".\n"; return a%2; int main( ) { int x = 1; int y = -2; int z = 3; x = my_fun(x,y,z); cout << "In main, x=" << x << " y=" << y << " z=" << z << ".\n"; return 0; Ans: In my_fun, a=0 b=3. In main, x=0 y=3 z= What is the output of the following program? Track the variables in a walkthrough table. bool test_fun (int x, int& y) {

10 if (x < y y > 1) return true; else { y = x%2; return false; int main( ) { int y = 1; for (int x= 0; x < 4; x++) { if ( test_fun(x, y) ) cout << "TRUE y=" << y << "\n"; else cout << "FALSE y=" << y << "\n"; return 0; Ans: TRUE y=1 FALSE y=1 FALSE y=0 FALSE y=1 23. Write a function grade2number that takes a student's letter grade without +/- (A,B,C,D,F) as a char and returns the corresponding numerical score in the GPA (4.0,3.0,2.0,1.0,0.0). You should handle the case when the student enters an invalid character (e.g. G) by return the number Use a switch statement. The function will be called as in the code below. char grade; cout << "Enter your letter grade (no +/-): "; cin >> grade; cout << "The corresponding numeric grade is: " << grade2number(grade); (As a follow-up practice exercise, you might want to consider how to handle grades with a + or -. It's a little tricky, because we can't switch on strings.) double grade2number ( char grade ) {

11 switch (grade) { case 'A': return 4.0; break; case 'B': return 3.0; break; case 'C': return 2.0; break; case 'D': return 1.0; break; case 'F': return 0.0; break; default: return -1.0; 24. Write a function largest2primes that finds the 2 largest prime factors of a given integer greater than one. Here we will report 1 as a prime number, if no larger prime factor is available. Your function should use a for loop. The function will be called as in the code below. int x; cout << "Enter an integer larger than one: "; cin >> x ; int factor1, factor2; largest2primes (x, factor1, factor2); cout << "The two largest prime factors of your number are "<< factor1 << " and " << factor2; void largest2primes (int x, int& factor1, int& factor2) { factor2 = 1; int divisor = 2; while (divisor <= x) { if (x%divisor == 0) { else return; x = x/divisor; factor1 = factor2; factor2 = divisor; divisor++;