Question

subject : basic programming with C++

Notes: please give me detailed answer so I could understand and learn from this, thank you very much

PL03; CO-5: Students have knowledge of modular programming / subprograms and can implement them in computer programs.; mark: 5%; 2. Given the following program! #include<iostream> using namespace std; (8,0 01234 5 6 7 8g int e[10]={6, 7, 4, 5, -1, 4, -1, 3, 1, 9); 2* Compute (8,91 int compute (int a, int b) { if (a == b) { return 1; Jelse if (e[a] == -1){ return 0; Helse return 2 * compute (e[a], b); } de Compute Answer the following questions with the program reference above a. What is the value of compute (8,4) b. If the value of the variable e is replaced as follows: int e[10] = {6, 7, 4, 5, 1, 4, 2, 6, -1, 8); What is the value of compute (1,4) In each question, write down the steps on how to get the results.

Answer 1

a)

The code for (a) part is as under:

#include <iostream>

using namespace std;

int e[10] = {6,7,4,5,-1,4,-1,3,1,9};

int compute(int a, int b)
{
if(a == b)
{
return 1;
}
  
else if(e[a] == -1)
{
return 0;
}
  
else
{
return 2*compute(e[a],b);
}
}

int main()
{
cout<<compute(8,4); //declaration of the question statement for execution

return 0;
}

Step by Step explanation:

> The values of a and b will be checked i.e. a=8 and b=4;

> As a != b, the first if statement will be skipped and moved to the next step.

> Now, the else if statement will be checked and as e[8] != -1 it will be skipped as well.

> Now, it will move to the else statement and will be executed.

Now, as we know that the question is using recursion therefore, the explanation of the recursion is as follows:

> compute(a,b) we will represent it as c(a,b) where a=8 and b=4

> Now, for the first recursion c(8,4) is as such that it will go to the else statement(already discussed above) i.e. 2*compute(e[a],b)

> There, the value it ill have will become c(e[8],4) which is equal to c(1,4) as the number at location e[8]=1. Now, a=1, b=4

> As we see again it will go to else statement 2*compute(e[a],b); where the new values for c(a,b) will be, c(7,4).

>As we see again it will go to else statement 2*compute(e[a],b); where the new values for c(a,b) will be, c(3,4)

>As we see again it will go to else statement 2*compute(e[a],b); where the new values for c(a,b) will be, c(5,4)

>As we see again it will go to else statement 2*compute(e[a],b); where the new values for c(a,b) will be, c(4,4) and now it fulfills the if statement and thus, returns 1, so now the result for the last step i.e. c(4,4) is 1 now the recursion will happen.

> Now, c(4,4) =1

c(5,4) = 2*c(4,4)=2

c(3,4)=2*c(5,4)=2*2=4

c(7,4)=2*c(3,4)=2*4=8

c(1,4)=2*c(7,4)=2*8=16

c(8,4)=2*c(1,4)=2*16=32 which is the desired result.

The output of this code is 32. Below is the screenshot attached of executed code with output.

Llı Result $g++ -o main *.cpp $main 32 == 9. Execute > Share main.cpp STDIN 1 #include <iostream> 2 3 using namespace std; 4 5 int e[10] = {6,7,4,5,-1,4,-1,3,1,9}; 6 7 int compute(int a, int b) 8- { 9 if(a == b) 10. { 11 return 1; 12 } 13 14 else if(e[a] -1) 15. { 16 return 0; 17 } 18 19 else 20 { 21 return 2*compute(e[a],b); 22 } 23 } 24 25 int main() 26 { 27 cout<<compute(8,4); 28 29 return 0; 30 }

b)

The code for proper execution of (b) is as under:

#include <iostream>

using namespace std;

int e[10] = {6,7,4,5,1,4,2,6,-1,8};

int compute(int a, int b)
{
if(a == b)
{
return 1;
}
  
else if(e[a] == -1)
{
return 0;
}
  
else
{
return 2*compute(e[a],b);
}
}

int main()
{
cout<<compute(1,4); //The code for the execution of the second part

return 0;
}

Breaking it to step by step explanation.

We will write compute(a,b) as c(a,b) for easy understanding.

Now, as we know that c(a,b) is not fulfilling either the if statement or the else if, so it will directly go to the else stataement. This is a question of recursion, so it will be solved using the same technique.

Let us break the recursion steps for better understanding:

> c(1,4) will directly go to else statement which is 2*compute(e[a],b), so it will become c(7,4).

> c(7,4) will directly go to else statement which is 2*compute(e[a],b), so it will become c(6,4).

> c(6,4) will directly go to else statement which is 2*compute(e[a],b), so it will become c(2,4).

> c(2,4) will directly go to else statement which is 2*compute(e[a],b), so it will become c(4,4).

> c(4,4) will go to if statement and will return 1.

> Therefore: c(4,4)=1

c(2,4)=2*c(4,4)=2*1=2

c(6,4)=2*c(2,4)=2*2=4

c(7,4)=2*c(6,4)=2*4=8

c(1,4)=2*c(7,4)=2*8=16, which is the desired output.

The output for this is 16. Below is the screenshot attached of executed code with output.

STDIN Llı Result Execute > Share main.cpp 1 #include <iostream> $g++ -o main *.cpp $main 16 3 using namespace std; 4 5 int e[10] = {6,7,4,5,1,4,2,6,-1,8}; 6 7 int compute(int a, int b) if(a == b) { return 1; } == -1) else if(e[a] { return 0; } 9 10 11 12 13 14 15 16 17 18 19 20. 21 22 23 24 25 26 27 28 29 30 else { return 2*compute(e[a],b); } } int main() { cout<<compute(1,4); return 0; }