#include <stdio.h>

int main() {
    int n, i;
    int a = 0, b = 1, next;

    printf("Enter number of terms: ");
    scanf("%d", &n);

    printf("Fibonacci Series:\n");

    for(i = 1; i <= n; i++) {
        printf("%d ", a);
        next = a + b;
        a = b;
        b = next;
    }

    return 0;
}

Input:
5
Output:
Fibonacci Series:
0 1 1 2 3

#include <stdio.h>

int main() {
    int n, i, pos[100], neg[100];
    int p = 0, ne = 0;

    printf("Enter number of elements: ");
    scanf("%d", &n);

    int arr[100];

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

    // Separate positive and negative numbers
    for(i = 0; i < n; i++) {
        if(arr[i] >= 0)
            pos[p++] = arr[i];
        else
            neg[ne++] = arr[i];
    }

    // Rearrange: positives first, then negatives
    printf("Rearranged array:\n");

    for(i = 0; i < p; i++) {
        printf("%d ", pos[i]);
    }

    for(i = 0; i < ne; i++) {
        printf("%d ", neg[i]);
    }

    return 0;
}

Input:
5
1 -2 3 -4 5
Output:
Rearranged array:
1 3 5 -2 -4

#include <stdio.h>

int isLeapYear(int year) {
    if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))
        return 1;
    return 0;
}

int main() {
    int day, month, year;
    int valid = 1;

    printf("Enter day month year: ");
    scanf("%d %d %d", &day, &month, &year);

    // Check month validity
    if (month < 1 || month > 12)
        valid = 0;

    // Days in months
    int daysInMonth[] = {31,28,31,30,31,30,31,31,30,31,30,31};

    // Adjust February for leap year
    if (isLeapYear(year))
        daysInMonth[1] = 29;

    // Check day validity
    if (day < 1 || day > daysInMonth[month - 1])
        valid = 0;

    if (valid)
        printf("Valid Date\n");
    else
        printf("Invalid Date\n");

    return 0;
}

A year is considered a leap year if:
• It is divisible by 4 but not divisible by 100, OR
• It is divisible by 400
In the program, February (month = 2) is assigned 29 days instead of 28 when the year is a leap year.