GATE IT 2008 | Question: 50

Question

Consider the C program below. What does it print?

# include <stdio.h>
# define swap1 (a, b) tmp = a; a = b; b = tmp
void swap2 ( int a, int b)
{
        int tmp;
        tmp = a; a = b; b = tmp;
 }
void swap3 (int*a, int*b)
{
        int tmp;
        tmp = *a; *a = *b; *b = tmp;
}
int main ()
{
        int num1 = 5, num2 = 4, tmp;
        if (num1 < num2) {swap1 (num1, num2);}
        if (num1 < num2) {swap2 (num1 + 1, num2);}
        if (num1 > = num2) {swap3 (&num1, &num2);}
        printf ("%d, %d", num1, num2);
}

• A. $5, 5$
• B. $5, 4$
• C. $4, 5$
• D. $4, 4$

Comments

if (num1 > num2) {swap1 (num1, num2);}
if (num1 < num2) {swap2 (num1 + 1, num2);}
if (num1 > = num2) {swap3 (&num1, &num2);}

 Now ans will be option (b) , First if condition is True so macros will be expanded and it will swap the value of num1 and num2 so num1 becomes 4 and num2 becomes 5 , 2nd if condition is False now come to 3 rd if  condition which is true and it's a real swap of num values using the call by reference, num1 becomes 5 and num 2 become 4. 

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K&R Pg.no. 89

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I think the question was edited multiple times as different asnwers over time are using different code (especially the if conditions).

This code is the one I found in gfg too as of the time I'm writing this.

Right answer is this accepted answer, where only statement 3 is getting executed.

        if (num1 < num2) {swap1 (num1, num2);}
        if (num1 < num2) {swap2 (num1 + 1, num2);}
        if (num1 > = num2) {swap3 (&num1, &num2);}

Answer 1

EXTRA(optional): https://onlinegdb.com/3h9SZeBoZ