GATE CSE 2005 | Question: 66

Question

Match each of the high level language statements given on the left hand side with the most natural addressing mode from those listed on the right hand side.$$\begin{array}{clcl} \text{(1)} &\text{$A[I] = B[J]$} & \qquad\text{(a)} &\text{Indirect addressing} \\ 
\text{(2)} &\text{while $(^*A\text{++});$} & \qquad\text{(b)} & \text{Indexed addressing} \\   
\text{(3)} & \text{int temp $= ^*x$} & \qquad\text{(c)} &\text{Auto increment}  \\ \end{array}$$

• A. $(1, c), (2, b), (3, a)$
• B. $(1, c), (2, c), (3, b)$
• C. $(1, b), (2, c), (3, a)$
• D. $(1, a), (2, b), (3, c)$

Comments

$\text{while(*A++)}$ tempted me to try the below code examples.

Note: $\text{A}$ is not an array but a pointer as $\text{A++}$ cannot be done with arrays because $\text{A++}$ is nothing but $\text{A=A+1}$ and in arrays value of $\text{A}$ is constant. But the same can be done with Pointers.

#include <stdio.h>
int main()
{
    int b[] = {3,2,0,1};
    int *A = b;
    //*A++ will be treated as *(A++) but increment of A will happen after using *A for condition check
    while(*A++){ 
        printf("%d\n",*A);    
    }
    return 0;
}
Output:
2
0

 

#include <stdio.h>
int main()
{
    int b[] = {3,2,0,1};
    int *A = b;
    //value of A[0] is checked for condition and then A[0] is incremented by 1, always checking A[0]
    while((*A)++){
        printf("%d\n",*A);    
    }
    return 0;
}
Output:
4
5
6
7
.
.
.

 

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@jatinmittal199510 Sir,

output of the first code will be  :2,0,1.

why will it not print 1?

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@Pranavpurkar This is because after *A = 0 is in while loop, it breaks out. Thus although later A++ makes it point to the 4^th element (i.e. 1) it can’t print it.

Answer 1

$C$ is the answer.

• $A[i] = B[j]$;     Indexed addressing
• while $(^*A++)$;      Auto increment
• temp $=^*x$;       Indirect addressing

Comments

Cristine

Priority of post-increment/decrement is higher than dereferencing operator in C...

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@akash.dinkar12 okay i got confused between *A++ and x=*A++ 

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Priority of post increment/decrement operator is higher than dereference operator but Priority of pre increment/decrement operator and dereference operator is same.

Ref: https://en.cppreference.com/w/c/language/operator_precedence