GATE CS 2003 Q2 — Programming in C

To determine which expressions can be used on the left-hand side (LHS) of an assignment statement without causing a compile-time error, we need to check if they evaluate to modifiable lvalues.

Given the declarations:

int *A[10], B[10][10];

• A is an array of 10 pointers to int (type: int *[10]).
• B is a 2D array of integers (type: int[10][10]).

Analyzing the Expressions:

1. Expression I: A[2]
   • A[2]` represents the $3^{\text{rd}}$ element of the array A.
   • Its type is int * (pointer to integer).
   • Since it is a pointer variable stored in an array, it is a modifiable lvalue. We can assign an address to it (e.g., A[2] = &x;).
   • No compile-time error.
2. Expression II: A[2][3]
   • This is equivalent to *(A[2] + 3).
   • Since A[2] is of type int *, dereferencing A[2] + 3 yields an int.
   • An integer variable is a modifiable lvalue. We can assign an integer value to it (e.g., A[2][3] = 5;).
   • No compile-time error.
3. Expression III: B[1]
   • B[1] represents the $2^{\text{nd}}$ row of the 2D array B.
   • Its type is int[10] (an array of 10 integers).
   • In C, an array name or sub-array expression acts as a constant pointer to its first element and is not a modifiable lvalue. We cannot assign to an entire array directly (e.g., B[1] = ptr; is invalid).
   • Causes a compile-time error.
4. Expression IV: B[2][3]
   • This represents a specific element in the 2D array B.
   • Its type is int.
   • An individual array element of a primitive type is a modifiable lvalue. We can assign an integer value to it (e.g., B[2][3] = 10;).
   • No compile-time error.

Thus, expressions I, II, and IV will not produce compile-time errors when used on the LHS of an assignment.