For the C++ program show on the next page, answer the questions that follow

105 views 23/09/202111/10/2021 admin 0 Comments C++ program, names are in scope, variables are live

Question

For the C++ program show on the next page, answer the questions that follow. The names g, j, x, and y are declare multiple times. So Distinguish uses of these names using line numbers where they were declare as subscripts.
a. At point A in the program, what names are in scope?
b. At point A in the program, what variables are live?
c. At point B in the program, what names are in scope?
d. At point B in the program, what variables are live?
Code for Problem III.

int g;
int h;
int bar(int x, int y) {
int f = x + y;
int g = 2 * h;
while (f < 0) {
int x = f - 1;
int y = g - 1;
g = x + y;
f--;
}
// Point A
f++;
int z = f * g;
return z;
}
int j = g + h;
void print(int v);
int foo(int a) {
int x = a * 2;
// Point B
int r = bar(a, x);
return r;
}
int main() {
int j = 3;
int k = 4;
int m = foo(j + k);
print(m);
return 0;
}

Summary

{x, y, g, h, z, f} are the variables that have a scope at point A.
‘g’ and ‘h’ are the variables that are live under point A.
{g, h, a, x, r, j} are the variables that can be accessed under point B.
{g, h, j} are the variables that are live under point B.

Explanation

Q) At point A in the program, what names are in scope?

At line numbers, 16, 17, and 18 there are total of three statements at points A which are in the function naming as bar().
So We will call the variable in scope if they can be accessed at the point.
‘g’ and ‘h’ are declare global so they can be accessed anywhere throughout the program.
‘f’ is in the local scope as it is declared inside the function. so ‘z’ also declares here.
‘x’ and ‘y’ are passed as arguments to the function so that they are in the local scope.
Hence {x, y, g, h, z, f} is the variable that can be accessed under point A

Q) At point A in the program, what variables are live?

Live variable means the variable which holds the value which can be use in the program.
‘z’ variable is returned when there is a function call, on line number 18.
At point A there are two variables naming as ‘g’ and ‘h’. And they are live which will be used in the program.
‘f’, ‘x’, and ‘y’ are in the local scope that’s why they cannot be used in the program.
Hence the variable ‘g’ and ‘h’ are live on point A.

Q) At point B in the program, what names are in scope?

On Point B, on line 28 and 29 there is 2 statements in the function.
That statements are in the function foo()
Here we passed a parameter with the value of ‘a’ so that it has local scope in point B.
So next global variables can e accessed at any point of the program. Global variables are ‘g’ and ‘h’.
Variable ‘r’ also declares so that it can have a local scope, along with the variable ‘X’ which is in the function foo.
‘j’ declares {g, h, a, x, r, j} are the variables that can be accessed on point B.
outside the function such that it is non-local scope.

Q) At point B in the program, what variables are live?

Live variable means the variable which holds the value which can be used in the program.
So When we called a function foo it returned a ‘r’ which is variable. So that it can be on line no 29.
At point B there are two variables naming as ‘g’ and ‘h’. And they are live which will be used in the program.
Whereas ‘j’ variable can also be use in program.
Hence variables {g, h, j} are live under the point B.

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