Week 6: Arrays, Randomness, and Control Flow (solution)

Exercise 1: Count how many even numbers are in an array.

1. Ask the user to enter 10 integers into a 1D array.
2. Print how many of them are even.

#include <stdio.h>

int main(void) {
    int arr[10], even = 0;
    for (int i = 0; i < 10; i++) {
        scanf("%d", &arr[i]);
        even += (arr[i] % 2 == 0);
    }
    printf("Number of even values: %d\n", even);
    return 0;
}

Example Output:

Number of even values: 4

Exercise 2: Calculate the sum of a 2D array.

1. Ask the user to input a 3x3 matrix
2. Print the total sum of all elements.

#include <stdio.h>

int main(void) {
    int arr[3][3], sum = 0;
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++) {
            scanf("%d", &arr[i][j]);
            sum += arr[i][j];
        }
    printf("Sum: %d\n", sum);
    return 0;
}

Example Output:

Sum: 45

Exercise 3: CFill an array with random numbers and find the maximum.

1. Use rand() to generate 10 random numbers
2. Print the largest number

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void)
{
    int arr[10], max;
    srand(time(0));

    for (int i = 0; i < 10; i++)
    {
        arr[i] = rand() % 100;
        printf("arr[%d]: %d\n", i, arr[i]);
        if (i == 0 || arr[i] > max)
            max = arr[i];
    }

    printf("Max: %d\n", max);
    return 0;
}

Example Output:

Max: 92

Exercise 4: Work with Variable-Length Arrays.

1. Ask the user how many elements they want to enter
2. Create a VLA and store those values
3. Print them in entered order

#include <stdio.h>

int main(void)
{
    int n;
    printf("Enter the number of elements: ");
    scanf("%d", &n);

    int arr[n];

    printf("Enter the elements:\n");
    for (int i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    printf("The elements in entered order are:\n");
    for (int i = 0; i < n; i++)
    {
        printf("%d ", arr[i]);
    }

    return 0;
}

Example Output:

Enter the number of elements: 5
Enter the elements:
1
2
3
4
5
The elements in entered order are:
1 2 3 4 5

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Bonus Challenge: Matrix Diagonal Sum

Ask the user to input a 3x3 matrix and print the sum of the diagonal elements.