Time due: 11:00 PM Tuesday, May 27
Go through the following sections of the class zyBook, doing the Participation Activities and Challenge Activities. We will be looking at whether you have ever successfully completed them; it does not matter how many attempts you make before a successful completion (or how many attempts you make after a successful completion if you want to experiment).
This project is designed to help you master pointers. To that end, you'll get the most out of it by working through the problems by hand. Only after that should you resort to running the programs (and stepping through them with the debugger) to check your understanding. Remember, on the final exam you'll have to be able to do problems like this by hand.
This "project" is more like a homework. There are five problems. In problems that ask you to change code, make the few changes necessary to fix the code without changing its overall approach. For example, don't fix the program in problem 1a by changing it to
int main()
{
cout << " 30 20 10" << endl;
}
The subparts to this problem involve errors in the use of pointers.
This program is supposed to write
30 20 10, but
it doesn't. Find all of the bugs and show a fixed version of the program:
int main()
{
int arr[3] = { 5, 10, 15 };
int* ptr = arr;
*ptr = 10; // set arr[0] to 10
*ptr + 1 = 20; // set arr[1] to 20
ptr += 2;
ptr[0] = 30; // set arr[2] to 30
while (ptr >= arr)
{
ptr--;
cout << ' ' << *ptr; // print values
}
cout << endl;
}
The findDisorder function is supposed to find the first item
in an array that is less than the element preceding it, and set the
p parameter to point to that item so the caller can know the
location of that item. Explain why this function won't do that, and show a
way to fix it. Your fix must be to the function only; you must not change
the the main routine below in any way, yet as a result of your fixing the
function, the main routine below must work correctly.
void findDisorder(int arr[], int n, int* p)
{
for (int k = 1; k < n; k++)
{
if (arr[k] < arr[k-1])
{
p = arr + k;
return;
}
}
p = nullptr;
}
int main()
{
int nums[6] = { 10, 20, 20, 40, 30, 50 };
int* ptr = &nums[0];
findDisorder(nums, 6, ptr);
if (ptr == nullptr)
cout << "The array is ordered" << endl;
else
{
cout << "The disorder is at address " << ptr << endl;
cout << "It's at position " << ptr - nums << endl;
cout << "The item's value is " << *ptr << endl;
}
}
The hypotenuse function is correct, but the main function has a
problem. Explain why it may not work, and show a way to fix it. Your fix must
be to the main function only; you must not change the hypotenuse
function in any way.
#include <iostream>
#include <cmath>
using namespace std;
void hypotenuse(double leg1, double leg2, double* resultPtr)
{
*resultPtr = sqrt(leg1*leg1 + leg2*leg2);
}
int main()
{
double* p;
hypotenuse(1.5, 2.0, p);
cout << "The hypotenuse is " << *p << endl;
}
The match function is supposed to return true if and only if
its two C string arguments have exactly same text. Explain what the problems
with the implementation of the function are, and show a way to fix them.
// return true if two C strings are equal
bool match(const char str1[], const char str2[])
{
while (str1 != 0 && str2 != 0) // zero bytes at ends
{
if (str1 != str2) // compare corresponding characters
return false;
str1++; // advance to the next character
str2++;
}
return str1 == str2; // both ended at same time?
}
int main()
{
char a[20] = "Hong";
char b[20] = "Hung";
if (match(a,b))
cout << "They're the same!\n";
}
This program is supposed to write 1 4 9 16 25 36 49 64 81 100 ,
but it probably does not. What is the program doing that is incorrect? (We're
not asking you explain why the incorrect action leads to the particular
outcome it does, and we're not asking you to propose a fix to the problem.)
#include <iostream>
using namespace std;
int* computeSquares(int& n)
{
int arr[10];
n = 10;
for (int k = 0; k < n; k++)
arr[k] = (k+1) * (k+1);
return arr;
}
void f(int b)
{
int junk[1000];
for (int k = 0; k < 1000; k++)
junk[k] = b + k;
}
int main()
{
int m;
int* ptr = computeSquares(m);
f(123400000);
for (int i = 0; i < m; i++)
cout << ptr[i] << ' ';
}
For each of the following parts, write a single C++ statement that performs
the indicated task. For each part, assume that all previous statements
have been executed (e.g., when doing part e, assume the statements
you wrote for parts a through d have been executed). For each part, do not
use any variable names or string literals not mentioned in that part (e.g.,
if the part doesn't mention fp or "tuna", do not
use fp or "tuna" in your answer).
fp that can point to a
variable of type string.fish to be a 5-element array of strings.fp variable point to the last element of
fish.fp equal to "yellowtail", using
the * operator.fp pointer, and without using square
brackets, set the fourth element (i.e., the one at position 3) of the
fish array to have the value "salmon".fp pointer back by three strings.fish,
set the third element (i.e., the one at position 2) of the fish
array to have the value "wahoo". (You may use fp.)* operator or the name
fish, but using square brackets, set the string pointed to by
fp to have the value "tang".== operator in the initialization expression,
declare a bool variable named d and initialize it with an
expression that evaluates to true if fp points to the
string at the start of the fish array, and to false
otherwise.* operator in the initialization expression,
but no square brackets, declare a bool variable named b and
initialize it to true if the string pointed to by fp is equal
to the string immediately following the string pointed to by
fp, and false otherwise. Do not use the name
fish
Rewrite the following function so that it returns the same result, but does
not increment the variable ptr. Your new program must not use
any square brackets, but must use an integer variable to visit each double
in the array. You may eliminate any unneeded variable.
double computeAverage(const double* scores, int nScores)
{
const double* ptr = scores;
double tot = 0;
while (ptr != scores + nScores)
{
tot += *ptr;
ptr++;
}
return tot/nScores;
}
Rewrite the following function so that it does not use any square brackets (not
even in the parameter declarations) but does use the integer variable
k. Do not use any of the <cstring> functions
such as strlen, strcpy, etc.
// This function searches through str for the character chr.
// If the chr is found, it returns a pointer into str where
// the character was first found, otherwise nullptr (not found).
const char* findTheChar(const char str[], char chr)
{
for (int k = 0; str[k] != 0; k++)
if (str[k] == chr)
return &str[k];
return nullptr;
}
Now rewrite the function shown in part b so that it uses neither square
brackets nor any integer variables. Your new function must not use any
local variables other than the parameters. Do not use any of the
<cstring> functions such as strlen,
strcpy, etc.
What does the following program print and why? Be sure to explain why each line of output prints the way it does to get full credit.
#include <iostream>
using namespace std;
int* minimart(int* a, int* b)
{
if (*a < *b)
return a;
else
return b;
}
void swap1(int* a, int *b)
{
int* temp = a;
a = b;
b = temp;
}
void swap2(int* a, int *b)
{
int temp = *a;
*a = *b;
*b = temp;
}
int main()
{
int array[6] = { 5, 3, 4, 17, 22, 19 };
int* ptr = minimart(array, &array[2]);
ptr[1] = 9;
ptr += 2;
*ptr = -1;
*(array+1) = 79;
cout << "diff=" << &array[5] - ptr << endl;
swap1(&array[0], &array[1]);
swap2(array, &array[2]);
for (int i = 0; i < 6; i++)
cout << array[i] << endl;
}
Write a function named deleteG that accepts one character
pointer as a parameter and returns no value. The parameter is a C string.
This function must remove all of the upper and lower case 'g' letters from
the string. The resulting string must be a valid C string.
Your function must declare no more than one local variable in addition to the
parameter; that additional variable must be of a pointer type. Your function
must not use any square brackets and must not use any of the
<cstring> functions such as strlen,
strcpy, etc.
int main()
{
char msg[100] = "I recall the glass gate next to Gus in Lagos, near the gold bridge.";
deleteG(msg);
cout << msg; // prints I recall the lass ate next to us in Laos, near the old bride.
}
You won't turn anything in through the CS 31 web site for Part 1; the zyBook system notes your successful completion of the PAs and CAs. For Part 2, prepare your solutions to these homework problems as a single Word document named hw.docx or a plain text file named hw.txt. Put that file in a zip file. By Monday, May 26, there will be a link on the class webpage that will enable you to turn in your zip file.