GATE CS 2017 Set 1 Q53 — Programming in C

To find the output of the program, let's trace the execution step-by-step:

1. In the main() function, we have:
   • x = "abc", so strlen(x) = 3
   • y = "defgh", so strlen(y) = 5
2. We call printlength(x, y), where s points to "abc" and t points to "defgh".
3. Inside printlength, we have:

   unsigned int c = 0;
   int len = ((strlen(s) - strlen(t)) > c) ? strlen(s) : strlen(t);

4. The function strlen returns a value of type size_t, which is an unsigned integer type.
   • When we perform strlen(s) - strlen(t), we are subtracting two unsigned integers: $3 - 5$.
   • In unsigned arithmetic, $3 - 5$ does not result in $-2$. Instead, it underflows to a very large positive value: $$3 - 5 \equiv -2 \equiv 2^{32} - 2 = 4294967294 \quad \text{(on a 32-bit system)}$$
5. The comparison (strlen(s) - strlen(t)) > c becomes: $$4294967294 > 0$$ Since this inequality is true, the ternary operator selects the first expression: strlen(s).
6. Thus, len is assigned the value of strlen(s), which is 3.

The program prints 3.