GATE CSE 2020 | Question: 48

Question

Consider the following C functions.

int tob (int b, int* arr) { int i; for (i = 0; b>0; i++)  { if (b%2)  arr [i] = 1;        else      arr[i] = 0;        b = b/2;   } return (i); }

int pp(int a, int b)  { int  arr[20]; int i, tot = 1, ex, len;     ex = a;     len = tob(b, arr);     for (i=0; i<len ; i++) {          if (arr[i] ==1)              tot = tot * ex;         ex= ex*ex;     } return (tot) ; }

The value returned by $pp(3,4)$ is _______.

Comments

silly mistake : when b%2=0 then else part will execute, not if  :(

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instead of $return$ $(tot)$ if we write $ return$ $(ex) $
then answer is $6561 $
$ex $$=$$ 81 $$*$ $81$$ =$$ 6561$

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@Lunar..us bro us 

 

Answer 1

Answer $: 81$

$pp(3,4)$

• $a=3, b=4 , \text{tot} = 1;$

len = tob(4, array) will return 3 with array set as $001$ as array is updated only once when  b%2 != 0). The for loop actually iterates $3$ times for $b = 4, b = 2$ and $b=1,$ and only when $b=1,$ arr[i] is updated.

Now pp will run for loop 3 times:

1. $\text{arr}[0] = 0.$ So, $\text{ex} = 3\ast 3 = 9$
2. $\text{arr}[1] = 0.$ So, $\text{ex} = 9\ast 9 = 81$
3. $\text{arr}[1] = 1.$ So, $\text{tot} = 1\ast 81 = 81$

Comments

Milan1999 Anju Mehral

in tob() : initially i=0;

if(4%2) ---→ if(0) so, it execute else statement… a[0] = 0  then b=2, i =1;

if(2%2) ---→ if(0) so, it execute else statement… a[1] = 0  then b=1, i=2;

if(1%2) ---→ if(1) so, it execute if statement….. a[2] = 1 then b=0, i=3;

and for loop break and return(i=3) to the calling function…

i.e, len = 3;

 

 

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if it satifies the 'if' condition, why would it execute the else statement?

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@avanyaokok The tob function takes b=4 

• i = 0:

  • b is 4 (even). arr[0] = 0.

  • b becomes 4 / 2 = 2.

• i = 1:

  • b is 2 (even). arr[1] = 0.

  • b becomes 2 / 2 = 1.

• i = 2:

  • b is 1 (odd). arr[2] = 1.

  • b becomes 1 / 2 = 0.

• The loop terminates as b is now 0. The function returns the final value of i, which is 3

Look in the question carefully , that in if condition of tob it is b%2 which will be 0 in case of even and eventually not executing the if condition and jump to else case.

Hope it helps !!!
 

Answer 2

THIS ILLUSTRATION MAY HELP😀

Answer 3

Answer: 81

Comments

@Bhupendra i will be 3 after the last iteration.

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rt.. !! thanks

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same i also got 27

Answer 4

1. The function tob(4, arr) sets the initial values of the first three indices of the array as 0, 0, and 1
2. The function returns index 3 after setting these values.
3. In each iteration of the for loop, whenever an array index has a value of 1, the result 3 * 3 (i.e., ex * ex) is multiplied by the variable tot.
4. The final value of tot is returned, which computes the power of 3, specifically 3^4 = 81.
5. In the GATE exam, don't rush to solve programming questions on paper immediately.
6. Take 10-15 seconds to observe the program and understand what is happening before proceeding.
7. After analyzing, solve the problem carefully and double-check your final answer to ensure its correctness.
8. In this case, the program computes 3^4, so the correct answer is 81.

Answer 5

https://ideone.com/Aedsbd

Answer 6

Tob() - converts b to binary

pp (3,4) = 3^4 = 81