SSC IMD SA Mock 03 – Question 168

\(What is the output of the following ‘C’ language statements?

#include<stdio.h>
int main(){
int a=10,b=20,*p1=&a,*p2=&b;
printf("Before : **p1=%d **p2=%d",*p1,*p2);
*p1=*p1+*p2;
*p2=*p1-*p2;
*p1=*p1-*p2;
printf("\nAfter : **p1=%d **p2=%d",*p1,*p2);
return 0;
}

\)

• Before : **p1=10 **p2=20
  After : **p1=20 **p2=10
• Before : **p1=20 **p2=10
  After : **p1=10 **p2=20
• Before : *p1=10 *p2=20
  After : *p1=20 *p2=20
• Before : p1=10 p2=20
  After : p1=20 p2=10

\(Trace of the C code:
1. `a = 10`, `b = 20`. `p1` points to `a`, and `p2` points to `b`. Thus, `*p1 = 10` and `*p2 = 20`.
2. The first `printf` prints the string literal with the values of `*p1` and `*p2`:
`Before : **p1=10 **p2=20`
3. Swapping logic using pointer dereferencing:
– `*p1 = *p1 + *p2;` ⟹ `a = 10 + 20 = 30`
– `*p2 = *p1 – *p2;` ⟹ `b = 30 – 20 = 10`
– `*p1 = *p1 – *p2;` ⟹ `a = 30 – 10 = 20`
After these operations, `*p1` is 20 and `*p2` is 10 (the values of `a` and `b` are swapped).
4. The second `printf` prints:
`\nAfter : **p1=20 **p2=10`\)

Therefore, the correct option is **a)**.