GATE CS 2020 Set 1 — Question 58
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Programming & Data Structures → C Programming → Arrays & Strings in C
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Question
Consider the following C functions.The value returned by pp(3, 4) is ________.
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);
}
Correct answer
81 to 81
Solution
The function
For
tob converts integer b to its binary representation in arr (LSB at index 0) and returns the number of bits.For
b=4 (binary 100), arr is {0, 0, 1} and len is 3.The function pp computes using the binary exponentiation (exponentiation by squaring) method.extracks .totaccumulates the product when the -th bit is 1.
pp(3, 4):i=0: bit is 0.exbecomes .i=1: bit is 0.exbecomes .i=2: bit is 1.totbecomes .exbecomes .
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