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

#define SAMPLE_COUNT 5

int main() {
    srand((unsigned int)time(NULL));
    
    for (int idx = 0; idx < SAMPLE_COUNT; ++idx) {
        int random_value = rand() % 100 + 1;
        printf("20490042%04d\n", random_value);
    }
    
    return 0;
}

This program produces five pseudorandom integers between 1 and 100 inclusive. Each is formatted as a zero-padded four-digit suffix appended to the prefix 20490042, yielding values in the range 204900420001 to 204900420100.

#include <stdio.h>

int main() {
    int selection;
    int units;
    float balance = 0.0f;
    float tendered;
    float difference;

    while (1) {
        printf("\nBeverage Dispenser Menu:\n");
        printf("1. Cola — ¥3.00 per unit\n");
        printf("2. Sprite — ¥3.00 per unit\n");
        printf("3. Orange Juice — ¥5.00 per unit\n");
        printf("4. Mineral Water — ¥2.00 per unit\n");
        printf("0. Exit transaction\n");
        printf("Select item: ");
        scanf("%d", &selection);

        if (selection == 0) break;

        if (selection < 1 || selection > 4) {
            printf("Invalid selection. Try again.\n");
            continue;
        }

        printf("Quantity: ");
        scanf("%d", &units);

        if (units < 0) {
            printf("Quantity must be non-negative.\n");
            continue;
        }

        switch (selection) {
            case 1:
            case 2:
                balance += 3.0f * units;
                break;
            case 3:
                balance += 5.0f * units;
                break;
            case 4:
                balance += 2.0f * units;
                break;
        }

        printf("Amount tendered: ¥");
        scanf("%f", &tendered);

        difference = tendered - balance;
        printf("Subtotal: ¥%.2f\n", balance);
        printf("Change due: ¥%.2f\n", difference);

        balance = 0.0f;
    }

    printf("Thank you for shopping!\n");
    return 0;
}

The vending machine simulator accumulates cost per selection using integer-based quantity input and floating-point pricing. Invalid inputs trigger appropriate feedback, and break terminates the loop on exit request while continue skips invalid iterations without exiting.

#include <stdio.h>

int main() {
    char signal;
    printf("Enter traffic light color (g/y/r): ");
    scanf(" %c", &signal);

    switch (signal) {
        case 'g':
        case 'G':
            printf("Proceed.\n");
            break;
        case 'y':
        case 'Y':
            printf("Prepare to stop.\n");
            break;
        case 'r':
        case 'R':
            printf("Stop immediately.\n");
            break;
        default:
            printf("Unrecognized signal. Verify input.\n");
            break;
    }

    return 0;
}

This implementation handles both uppercase and lowercase input for robustness and includes a fallback message for unrecognized characters.

#include <stdio.h>

int main() {
    double entry;
    double total = 0.0;
    double highest = 0.0;
    double lowest = 0.0;
    double average;
    int tally = 0;

    printf("Enter daily expenses (−1 to finish):\n");

    while (1) {
        scanf("%lf", &entry);
        if (entry == -1.0) break;

        if (tally == 0) {
            highest = entry;
            lowest = entry;
        } else {
            if (entry > highest) highest = entry;
            if (entry < lowest) lowest = entry;
        }

        total += entry;
        ++tally;
    }

    if (tally > 0) {
        average = total / tally;
        printf("Total spending: ¥%.1f\n", total);
        printf("Highest single expense: ¥%.1f\n", highest);
        printf("Lowest single expense: ¥%.1f\n", lowest);
        printf("Average per transaction: ¥%.1f\n", average);
    } else {
        printf("No entries recorded.\n");
    }

    return 0;
}

The expense tracker initializes bounds only after the first valid entry, avoiding assumptions about initial values. It also guards against division-by-zero when no data is entered.

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

int main() {
    int target, guess;
    const int max_tries = 3;

    srand((unsigned int)time(NULL));
    target = rand() % 30 + 1;

    printf("Guess your lucky day in April 2025 (1–30)\n");
    printf("You have %d attempts. Begin:\n", max_tries);

    for (int attempt = 0; attempt < max_tries; ++attempt) {
        printf("Attempt %d/%d: ", attempt + 1, max_tries);
        scanf("%d", &guess);

        if (guess == target) {
            printf("Congratulations! You guessed correctly!\n");
            return 0;
        } else if (guess < target) {
            printf("Too early — your lucky day is later.\n");
        } else {
            printf("Too late — your lucky day is earlier.\n");
        }
    }

    printf("All attempts exhausted. Your lucky day is %d.\n", target);
    return 0;
}

The guessing game uses clear attempt counting and contextual hints based on numeric comparison, with early termination upon success.

#include <stdio.h>

int main() {
    int height;
    printf("Enter number of rows for inverted triangle: ");
    scanf("%d", &height);

    for (int row = height; row >= 1; --row) {
        // Leading spaces
        for (int pad = 0; pad < height - row; ++pad) {
            printf("      ");
        }

        // First line: '0'
        for (int col = 0; col < 2 * row - 1; ++col) {
            printf(" 0   ");
        }
        printf("\n");

        // Second line: '<H>'
        for (int pad = 0; pad < height - row; ++pad) {
            printf("      ");
        }
        for (int col = 0; col < 2 * row - 1; ++col) {
            printf("<H>  ");
        }
        printf("\n");

        // Third line: 'I I'
        for (int pad = 0; pad < height - row; ++pad) {
            printf("      ");
        }
        for (int col = 0; col < 2 * row - 1; ++col) {
            printf("I I   ");
        }
        printf("\n");
    }

    return 0;
}

The pattern printer constructs a inverted triangular layout with three distinct symbol rows per level (0, <H>, I I) and consistent horizontal spacing.