1. ㅎㅎ Fifth step for Learning C++ Programming Pointers Homework solution
Review

2. A pointer is a variable that holds the address of something else.
Pointers
A pointer is a variable
that holds the address
of something else.
...
MEMORY 1 2 3 4 5
81345
81346
81347
Address
int foo;
int *x;
foo = 123;
x = &foo;
foo
123 x 3
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3. Assigning a value to a dereferenced pointer
A pointer must have a value before you can dereference it (follow the pointer).
int *x;
*x=3;
int foo;
int *x;
x = &foo;
*x=3;
x doesn’t point to anything!!!
ERROR!!!
this is fine
x points to foo
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4. [ practice 1 first pointer variable ]

5. [ explain 1 first pointer variable ]

6. [ practice 2 initialize a pointer ]

7. [ explain 2 initialize a pointer ]

8. [ practice 3 Arrays of Pointers ]

9. [ explain 3 Arrays of Pointers ]
= {a, b};

10. Exercise 1 HomeWork1 Condition Result (x>y) && !y
Given the following assignment of variables to values:
Fill in the result values of the conditions in the table below
Condition
Result
(x>y) && !y
(item>MIN)||(DAY!=’M’) 1
((num*128)<power)&&y
(!(power!=MAX))&&(Sens==num)
((y+x)<num)||(DAY==’M’)
(Sens*(!y))!=0
(!x||y)&&(!y||x)
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11. HomeWork1
Exercise 2
Write a program in C++ that performs the following tasks:
Read three integer values using cin.
Determine the maximum of the three values entered by the user.
Print the maximum of this three values using cout.
int main() {
int a, b, c;
cout << "Enter the first integer : " ;
cin >> a;
cout << "Enter the second integer : " ;
cin >> b;
cout << "Enter the third integer : " ;
cin >> c ;
cout << endl;
if((a > b) && (a > c))
cout << "Maximum integer is " << a <<endl; }
else if((b > c ) && (b > a))
cout << "Maximum integer is " << b <<endl;
else
cout << "Maximum integer is " << c << endl;
return 0;
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12. Exercise 3 HomeWork1 int main() { int a, sum = 0; do
Write a program that asks the user to type numbers. After each entry,
the program should report the cumulative sum of the entries.
The program should terminate when the user enters 0.
int main() {
int a, sum = 0; do
cout << "Enter the number : " ;
cin >> a;
sum = sum + a;
}while( a!=0);
cout << "Sum is " << sum << endl;
return 0; }
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13. HomeWork1
Exercise 4
Create a program to determine the GCD (Greatest Common Divisor) of two integers x and y using a ‘while loop’.
Formal description of the Euclidean algorithm
Input Two positive integers, a and b.
Output The greatest common divisor, g, of a and b.
Internal computation
If a<b, exchange a and b.
Divide a by b and get the remainder, r. If r=0, report b as the GCD of a and b.
Replace a by b and replace b by r. Return to the previous step.
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14. Exercise 4 HomeWork1 int main() { int a, b, r;
cout << "Enter the two integers to determine the GCD : ";
cin >> a >> b;
while((a < 0) || (b < 0)) {
cout << "Don't enter the negative number! Please.. enter again : "; }
if(a < b) {
int temp;
temp = a;
a = b;
b = temp;
do {
r = a % b;
if( r == 0) {
cout << "The GCD of a and b is "<< b << endl;
break;
else
b = r;
} while(1);
return 0;
Exercise 4
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15. HomeWork2
Exercise 1
1) Write a function that computes the value of the binomial coefficient
2) Embed your function into a little program that reads two integers n and r from std::cin and writes the value of the binomial coefficient to std::cout
int fac(int x) {
if(x <= 0)
return 1;
else
return x * fac(x-1); }
int bc(int n, int r)
return fac(n) / (fac(n-r)*fac(r));
void main()
int n, r;
std:: cout << "Enter two natural numbers: ";
std:: cin >> n >> r;
if(n < 0 && r < 0) do
std::cout << "Please again enter two natural numbers !! " <<std::endl;
std:: cout << "Enter two natrural number ";
std::cin >> n >> r;
} while(n < 0 || r < 0);
std::cout << "C(" << n << "," << r << ") = " << bc(n, r) << std::endl;
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16. Exercise 2 HomeWork2 void permutNumbers(int data[], int x, int n) {
Write a function permutNumbers that prints all n! many permutations of the numbers 1 to n on std::out.
Example: the output for permutNumbers (3) shall be: 123, 132, 213, 231, 312, 321
void permutNumbers(int data[], int x, int n) {
int k, temp;
if(x==n-1)
for(k=0; k<n; k++)
cout << data[k];
if(k==n)
cout << " "; }
else
for(k=x; k<n; k++)
temp=data[k];
data[k]=data[x];
data[x]=temp;
permutNumbers(data, x+1, n);
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17. cout << "Enter one natural number : "; cin >> a;
HomeWork2
Exercise 2
Write a function permutNumbers that prints all n! many permutations of the numbers 1 to n on std::out.
Example: the output for permutNumbers (3) shall be:
123, 132, 213, 231, 312, 321
int main() {
int a, i;
int data[MAX];
cout << "Enter one natural number : ";
cin >> a;
for(i=0; i<a; i++)
data[i] = i+1;
permutNumbers(data, 0, a);
return 0; }
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18. Exercise 1 HomeWork3 19 Given the following function definition:
int sum_down(int x) {
if (x >= 0)
x = x - 1;
int y = x + sum_down(x);
return y + sum_down(x); }
else
return 1;
a) What is this smallest integer value of the parameter x, so that the returned value is greater than ? 19
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19. while (x <= x_final) sum = (x - 1) + 2 * sum; x = x + 1; }
HomeWork3
Exercise 1
b) Rewrite the function, so that it is free of recursion. I.e. give an iterative definition on the
foundation of a loop-construct. TIP: First transform the recursive definition, so that you have just a single recursive call.
int sum_down_while(int x_final) {
int sum = 1; int x = 0;
while (x <= x_final)
sum = (x - 1) + 2 * sum;
x = x + 1; }
return sum;
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20. HomeWork3
Exercise 1 X
c) Assume that we change the parameter x to a reference parameter.
So we get: int sum_down(int &x)
Adapt your solution for b), so that it shows once again the same behaviour like the recursive
definition.
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21. Exercise 1 Error!! x is would be -1 HomeWork3
d) Is it ok to switch the type of the parameter x to unsigned int? Discuss your decision / give an argumentation.
int sum_down(unsigned int x) {
if (x >= 0)
x = x - 1;
int y = x + sum_down(x);
return y + sum_down(x); }
else
return 1;
Error!!
x is would be -1
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22. Exercise 1 Possible!! HomeWork3
e) Is it ok to switch the type of the parameter x to double? Discuss your decision / give an argumentation.
int sum_down(double x) {
if (x >= 0)
x = x - 1;
int y = x + sum_down(x);
return y + sum_down(x); }
else
return 1;
Possible!!
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23. Exercise 1 Error!! HomeWork3
f) Is it ok to switch the function head to int sum_down(const int x)? Discuss your decision / give an argumentation.
int sum_down(const int x) {
if (x >= 0)
x = x - 1;
int y = x + sum_down(x);
return y + sum_down(x); }
else
return 1;
Error!!
10/2013