Thread: Pointer Question

Hi,
I am having problem understand one of the questions in our midterm. It is related to pointers.

Code:

6. What is the output of the following program?
int f(int *x, int y) {
*x += 2; y += 1;
return *x + y;
}
int g(int x, int *y) {
*y = x++;
return x + *y;
}
int main( ) {
int x = 3, y = 4;
printf("%d ",f(&x, y));
printf("%d ",g(x, &y));
printf("%d %d \n",x, y);
return 0;
}
(A) 10 11 5 5 (B) 10 11 6 6 (C) 10 12 5 5 (D) 10 11 6 7

The answer is (A) but I get confused where did 11 come from.
Could someone please help me understand this.

Thanks
Sara

Originally Posted by sara.stanley

Hi,
I am having problem understand one of the questions in our midterm. It is related to pointers.

Code:

6. What is the output of the following program?
int f(int *x, int y) {
*x += 2; y += 1;
return *x + y;
}
int g(int x, int *y) {
*y = x++;
return x + *y;
}
int main( ) {
int x = 3, y = 4;
printf("%d ",f(&x, y));
printf("%d ",g(x, &y));
printf("%d %d \n",x, y);
return 0;
}
(A) 10 11 5 5 (B) 10 11 6 6 (C) 10 12 5 5 (D) 10 11 6 7

The answer is (A) but I get confused where did 11 come from.
Could someone please help me understand this.

Thanks
Sara

The reason is because once function f() returns in the first printf, the x variable contains a new value, because it was modified in f(), x on return contains 5. When the second printf executes, it calls g() with two arguments which each contain the values 5 and 4 respecively. In g(), y is assigned the value of x (which is 5) and then x is incremented, now x equals 6. When it adds x and y in the return statement, it produces the value 11 and returns that.

thanks alot I understand now. I was confused about this statment *y=x++;

basically what is doing is that it puts the value of x in y and x is updated.

I was thinking of this like this: