Mid Semester Practice Questions #

This practice set is in continuation of previous quiz-1 problem set and starts from Lecture-06 Strings and Arrays

Question 1: #

#include <stdio.h>
int main() {
    int marks[5] = {90, 85, 88, 92, 88};
    for (int i = 0; i <= 5; i++) {
        printf("%d ", marks[i]);
    }
    return 0;
}

What will happen when this code runs? Identify the error and explain why it occurs.

Question 2: #

#include <stdio.h>
int main() {
    char name1[5] = "Alice";
    char name2[5] = {'A','l','i','c','e'};
    printf("Length of name1: %lu\n", strlen(name1));
    printf("Length of name2: %lu\n", strlen(name2));
    return 0;
}

Predict the output. What is the difference between the two string initializations?

Question 3: #

#include <stdio.h>
int main() {
    char x = 127;
    char y = 1;
    char result = x + y;
    printf("x = %d, y = %d, result = %d\n", x, y, result);
    return 0;
}

What will be the output? Explain what happens during the addition in terms of two’s complement representation.

Question 4: #

#include <stdio.h>
int main() {
    int a = 12, b = 7;  // a = 1100, b = 0111 in binary
    printf("a & b = %d\n", ____);  // AND operation
    printf("a | b = %d\n", ____);  // OR operation  
    printf("a ^ b = %d\n", ____);  // XOR operation
    printf("a << 2 = %d\n", ____); // Left shift by 2
    return 0;
}

Fill in the blanks with the expected output values and show your binary calculations.

Question 5: #

#include <stdio.h>
int main() {
    float sum = 0.0f;
    for(int i = 0; i < 10; i++) {
        sum += 0.1f;
    }
    if(sum == 1.0f) {
        printf("Equal\n");
    } else {
        printf("Not Equal: %.10f\n", sum);
    }
    return 0;
}

What will be the output and why does this happen? How would you fix this comparison?

Question 6: #

#include <stdio.h>
int main() {
    int x = 0, y = 5;
    if(x++ > 0 && y++ > 3) {
        printf("Inside if\n");
    }
    printf("x = %d, y = %d\n", x, y);
    return 0;
}

What values will x and y have at the end? Explain the short-circuit evaluation behavior.

Question 7: #

#include <stdio.h>
#include <string.h>
int main() {
    char dest[5];
    char src[] = "Programming";
    strcpy(dest, src);
    printf("%s\n", dest);
    return 0;
}

What error will occur when this code runs? How would you fix it using strncpy?

Question 8: #

#include <stdio.h>
int gcd(int a, int b) {
    printf("gcd(%d, %d)\n", a, b);
    if (b == 0) return a;
    return gcd(b, a % b);
}
int main() {
    int result = gcd(24, 16);
    printf("Result: %d\n", result);
    return 0;
}

Trace through the recursive calls. What will be printed step by step?

Question 9: #

#include <stdio.h>
void selectionSort(int arr[], int n) {
    for(int i = 0; i < n-1; i++) {
        int minIndex = i;
        for(int j = ____; j < ____; j++) {
            if(arr[j] < arr[minIndex]) {
                minIndex = j;
            }
        }
        // Swap elements
        int temp = arr[i];
        arr[i] = ____;
        arr[minIndex] = ____;
    }
}

Fill in the blanks to complete the selection sort implementation.

Question 10: #

#include <stdio.h>
int binarySearch(int arr[], int low, int high, int key) {
    if (low > high) return -1;
    int mid = (low + high) / 2;
    if (arr[mid] == key) return mid;
    else if (arr[mid] > key)
        return binarySearch(arr, low, mid - 1, key);
    else
        return binarySearch(arr, mid + 1, high, key);
}
int main() {
    int arr[] = {1, 3, 5, 7, 9};
    int result = binarySearch(arr, 0, 4, 6);
    printf("Result: %d\n", result);
    return 0;
}

What will be the output when searching for 6? Trace through the recursive calls.

Question 11: #

#include <stdio.h>
int count = 0;
int fibonacci(int n) {
    count++;
    if (n == 0) return 0;
    if (n == 1) return 1;
    return fibonacci(n-1) + fibonacci(n-2);
}
int main() {
    int result = fibonacci(5);
    printf("F(5) = %d, Function calls: %d\n", result, count);
    return 0;
}

What will be the output? Why is this implementation inefficient for large values of n?

Question 12: #

#include <stdio.h>
int moves = 0;
void hanoi(int n, char from, char to, char aux) {
    if (n == 1) {
        moves++;
        printf("Move disk 1 from %c to %c\n", from, to);
        return;
    }
    hanoi(n-1, from, aux, to);
    moves++;
    printf("Move disk %d from %c to %c\n", n, from, to);
    hanoi(n-1, aux, to, from);
}
int main() {
    hanoi(3, 'A', 'C', 'B');
    printf("Total moves: %d\n", moves);
    return 0;
}

How many total moves will be printed for 3 disks? Can you derive the formula for n disks?

Question 13: #

#include <stdio.h>
void merge(int arr[], int l, int m, int r) {
    int n1 = m - l + 1;
    int n2 = r - m;
    int L[n1], R[n2];
    
    for (int i = 0; i < n1; i++) L[i] = arr[l + i];
    for (int j = 0; j < n2; j++) R[j] = arr[m + 1 + j];
    
    int i = 0, j = 0, k = l;
    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k++] = L[i++];
        } else {
            arr[k++] = R[j++];
        }
    }
    
    // What's missing here?
    // Fill in the blanks:
    while (i < n1) arr[k++] = ____;
    while (j < n2) arr[k++] = ____;
}

Fill in the missing code. What happens if these lines are omitted?

Question 14: #

#include <stdio.h>
int factorial(int n) {
    printf("Computing factorial(%d)\n", n);
    if (n = 1) return 1;  
    return n * factorial(n - 1);
}
int main() {
    int result = factorial(5);
    printf("Result: %d\n", result);
    return 0;
}

What is wrong with this code? What will happen when it runs and why?

Question 15: #

#include <stdio.h>
void generateBinary(int n, char str[], int pos) {
    if (pos == n) {
        str[n] = '\0';
        printf("%s\n", str);
        return;
    }
    
    str[pos] = '0';
    generateBinary(n, str, pos + 1);
    
    str[pos] = '1';
    generateBinary(n, str, pos + 1);
}
int main() {
    char str[10];
    generateBinary(3, str, 0);
    return 0;
}

What will be the complete output? How many binary strings will be printed and in what order?

Question 16: #

#include <stdio.h>
int power(int base, int exp) {
    if (exp == 0) return ____;
    if (exp == 1) return ____;
    
    if (exp % 2 == 0) {
        int half = power(base, ____);
        return half * half;
    } else {
        return base * power(base, ____);
    }
}
int main() {
    printf("2^8 = %d\n", power(2, 8));
    printf("3^5 = %d\n", power(3, 5));
    return 0;
}

Fill in the blanks to complete this optimized recursive power function.

Question 17: #

#include <stdio.h>
int arraySum(int arr[], int n) {
    if (n <= 0) return 0;
    return arr[n] + arraySum(arr, n - 1);  
}
int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int result = arraySum(arr, 5);
    printf("Sum = %d\n", result);
    return 0;
}

What is the error in this recursive sum function? What would be the incorrect result?

Question 18: Binary Strings with Exactly k Ones #

Problem Statement: Write a recursive program that prints all binary strings of length n with exactly k ones.

Example 1:

Input: n = 3, k = 2
Output:
```
011
101
110
```

Example 2:

Input: n = 4, k = 1
Output:
```
0001
0010
0100
1000
```

Question 19: All Permutations of Numbers 1 to n #

Problem Statement: Write a recursive program that prints all permutations of numbers from 1 to n.

Example 1:

Input: n = 3
Output:
```
1 2 3
1 3 2
2 1 3
2 3 1
3 1 2
3 2 1
```

Example 2:

Input: n = 2
Output:
```
1 2
2 1
```

Question 20: Balanced Parentheses Strings #

Problem Statement: Write a recursive program that prints all balanced parentheses strings of length 2n.

Example 1:

Input: n = 2
Output:
```
(())
()()
```

Example 2:

Input: n = 3
Output:
```
((()))
(()())
(())()
()(())
()()()
```

Question 21: All Subsets of n Distinct Elements #

Problem Statement: Take a sequence of n distinct elements as input, and print all subsets of the n element set formed by them.

Example 1:

Input: arr = [1, 2, 3]

Output:

{}
{1}
{2}
{1, 2}
{3}
{1, 3}
{2, 3}
{1, 2, 3}

Example 2:

Input: arr = [5, 10]
Output:
```
{}
{5}
{10}
{5, 10}
```

Question 22: All k-Element Subsets #

Problem Statement: Take a sequence of n distinct elements and a number k as input, and print all k element subsets of the n element set formed by them.

Example 1:

Input: arr = [1, 2, 3, 4], k = 2

Output:

{1, 2}
{1, 3}
{1, 4}
{2, 3}
{2, 4}
{3, 4}

Example 2:

Input: arr = [5, 10, 15], k = 1
Output:
```
{5}
{10}
{15}
```

Question 23: Count Subsets with Sum k #

Problem Statement: Given an array, count the number of subsets whose elements add up to k (return the count, don’t print the subsets).

Example 1:

Input: arr = [1, 2, 3, 4], k = 5
Output: 2
Explanation: Subsets {1, 4} and {2, 3} both sum to 5

Example 2:

Input: arr = [2, 4, 6, 8], k = 10
Output: 2
Explanation: Subsets {2, 8} and {4, 6} both sum to 10

Example 3:

Input: arr = [1, 1, 1, 1], k = 2
Output: 6
Explanation: Any combination of exactly 2 ones from the 4 available ones