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# Assignment #4: Parameter Passing and Python’s List Comprehensions

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CSE 305
Assignment #4:
Parameter Passing and Python’s List Comprehensions

Note: This assignment may be done by a pair of students.
1. Consider the following incorrect C program to compute the normal form of a rational number:
typedef struct {
int numr;
int denr;
} RATIONAL;
int main() {
RATIONAL r;
int normalize(RATIONAL r) {
int gcd(int x, int y) {
while (x != y)
if (x y)
x = x-y;
else y=y-x;
return x;
}
int g = gcd(r.numr, r.denr);
r.numr = r.numr/g;
r.denr = r.denr/g;
}
r.numr = 77;
r.denr = 88;
normalize(r);
printf(“%d/%d\n”, r.numr, r.denr);
}
a. Why does normalize not compute the normal form of the rational number 77/88?
b. Using call-by-reference for parameter r, show a corrected version of normalize along
with a suitable call on normalize so that the output is the correct normal form of
77/88.
Name your file rational2.c and submit it online. Include the answer for part (a) also
in the file as a comment at the top of the file.
2. Consider the following C function for carrying out the summation expressed by the operator ∑:
int sigma(int *k, int low, int high, int expr()) {
int sum = 0;
for (*k=low; *k<=high; (*k)++) {
sum = sum + expr();
}
return sum;
}
a. Write a main program that makes repeated use of sigma in order to compute and print out
the value of (parentheses added to clarify grouping) :

Name your file sigma.c and submit it online.
b. Consider the multiplication of two matrices, c = a x b, defined as:
(In original assignment, it was a[i,j]*b[j,k]. This typo has been corrected above.)
Define in C a procedure matmult that incorporates the above definition: translate the
universal quantifier using a for-loop and the operator ∑ using sigma. Test matmult with:
Use the following main procedure to test out your matmult definition. It suffices for matmult
to work with 2×2 matrices.
int main(){
int a = {{1,2}, {3,4}};
int b = {{5,6}, {7,8}};
int c;
matmult(a, b, c);
printf(“%d %d\n%d %d\n”,
c, c, c, c);
}
Name your file matrix.c and submit it online.
3. Consider the Python definition for ‘quicksort’ using list comprehensions:
def qsort(a):
if a == []: return []
left = [x for x in a[1:] if x < a]
right = [x for x in a[1:] if x = a]
return qsort(left) + [a] + qsort(right)
print(qsort([5,4,6,3,7,9,2,8,1,0]))
a. i. Replace the + operations in the above code by Python’s built-in append/extend operations.
ii. Replace the list comprehensions by equivalent code making use of Python list generators.
Use append/extend in your generated code.
Test your program to make sure it sorts correctly. Name the file qsort1.py, and submit it online.
b. Replace the list generators in qsort1.py by equivalent code making use of higher-order functions
and thunks.
Test your program to make sure it sorts correctly. Name the file qsort2.py, and submit it online.
Team-work and On-line Submission:
1. This assignment may be done by a team of at most two students. Write both student names at
the top of all program files when submitting them.
2. It is fine to do the assignment solo. Write your name at the top of each file and submit it.
End of Assignment #4

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