Question

Consider the following in C

int main() { float x = 3.14, *p = &x; int r, a = 2, b[] = {5, 6, 7}; <more code here> r = Foo(x, p, &a, b) <more code here> } int Foo(float x,float y, int *z, int *w) { <Foo's code goes here> } statement in Foo result (assigned value) modify Foo's AF variables modify main's AF variables statement in Foo result (assigned value) modify Foo's AF variables modify main's AF variables (Yes (Yes *y+= 1.86; or NO) or NO) (Yes (Yes z += 1; or NO) or NO) (Yes (Yes w[ 1 ] += 20; or NO) or NO) (Yes (Yes return (*z + *w); or NO) or NO) * For each statement from Foo below, list the resulting value. If the result is an address, just list "address". For return statements, list the returned value. Also determine if it affects Foo's activation frame variables, main's activation frame variables, or both. Consider each statement independently and non-cumulatively (i.e., as if it is the only statement in Foo).

Answer 1

Statement 1: *y += 1.86

• p is a variable of type float *, the value that it points to(variable x) incremented by 1.86. x in the main() function will change to 5.00.
• Also, since there is no modification in local variables or parameters of foo() there is no change in its AF.
• howver, the value of x changes, since this is a local variable in main() , the AF of main will change
• Answer:
• Result : x = 5
• change in foo() AF: NO
• change in main() AF: YES

statement 2: z+= 1

• Z points to the variable a in main().
• Which means, Z holds the address of a.
• if we increment z, the address will altered.
• So, only the parameter z will change, and there is no change to anything else.
• So, only the AF of foo() will be modified
• Answer:
• Result : z = address
• change in foo() AF: yes
• change in main() AF : no

statement 3: w[1] += 20.

• w is being passed as a integer pointer.
• altering w[1] will alter the value at *(w+1). So, w will be altered in main().
• 20 will be added to w[1], and the result will be w[1] = 6+20 = 26
• Answer:
• Result : w = {5,26,7}
• change in foo() AF: no
• change in main() AF: yes

statement 4: return *z + *w

• The values in *z and *w is being added and returned.
• The value of r in the main() function stores this return values, so it will be altered.
• The return value will be 2+5 = 7
• Answer:
• Result: 7
• change in foo() AF: no
• change in main() AF: yes