Random Number Generation and Formatting

Objective 1: Generate five random numbers with in the range 202400420001 to 202400420100 and output them.

Objective 2: Generate a random integer between 1 and 100.

Objective 3: Format numeric output to display exactly four digits, padding with leading zeros if necesary.

Objective 4: Use the currrent system time as a seed for the random number generator to ensure a different sequence of pseudo-random numbers on each program execution. Omitting this step results in the same sequence being gneerated across multiple runs.

Loop Control and State Manageemnt

Issue 1: In a cumulative purchase system, a customer's transaction amount incorrectly accumulates from the previous customer's total.

Issue 2: Implementing a control flow statement to skip the current iteration of a loop and proceed to the next one.

Traffic Signal Simulator Using Character Input

#include <stdio.h>
int main() {
    char signal_input;
    while (scanf("%c", &signal_input) != EOF) {
        getchar(); // Consume newline character
        if (signal_input == 'r') {
            printf("stop!\n");
        }
        else if (signal_input == 'g') {
            printf("go go go\n");
        }
        else if (signal_input == 'y') {
            printf("wait a minute\n");
        }
        else {
            printf("something must be wrong...\n");
        }
    }
    return 0;
}

Daily Expense Tracker with Statistics

#include<stdio.h>
int main()
{
    float expense, daily_total = 0.0, highest = 0.0, lowest = 20000.0;
    printf("Enter today's expenses. Input -1 to finish:\n");
    while (1) {
        scanf("%f", &expense);
        if (expense == -1) {
            break;
        }
        if (expense > 0 && expense < 20000) {
            daily_total += expense;
            if (expense > highest) {
                highest = expense;
            }
            if (expense < lowest) {
                lowest = expense;
            }
        }
    }
    printf("Total expenses for the day: %.1f\n", daily_total);
    printf("Highest single expense: %.1f\n", highest);
    printf("Lowest single expense: %.1f\n", lowest);
    return 0;
}

Triangle Type Classifier

#include <stdio.h>

int main() {
    int side1, side2, side3;
    while (scanf("%d%d%d", &side1, &side2, &side3) != EOF) {
        if (side1 + side2 > side3 && side1 + side3 > side2 && side2 + side3 > side1) {
            if (side1 == side2 && side2 == side3) {
                printf("Equilateral triangle\n");
            }
            else if (side1 == side2 || side1 == side3 || side2 == side3) {
                printf("Isosceles triangle\n");
            }
            else if (side1 * side1 + side2 * side2 == side3 * side3 || 
                     side1 * side1 + side3 * side3 == side2 * side2 || 
                     side2 * side2 + side3 * side3 == side1 * side1) {
                printf("Right triangle\n");
            }
            else {
                printf("Scalene triangle\n");
            }
        }
        else {
            printf("Not a valid triangle\n");
        }
    }
    return 0;
}

Lucky Day Guessing Game

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

int main() {
    int secret_day, user_guess, attempts = 0;
    srand(time(0));
    secret_day = rand() % 30 + 1;

    printf("Guess your lucky day in April 2026.\n");
    printf("You have 3 attempts. Enter your guess (1~30):");
    while (attempts < 3) {
        scanf("%d", &user_guess);
        attempts++;
        if (user_guess == secret_day) {
            printf("Correct! :)\n");
            break;
        }
        else if (attempts < 3) {
            if (user_guess > secret_day) {
                printf("Your guess is too late. Your lucky day is earlier. Guess again (1~30):");
            }
            else {
                printf("Your guess is too early. Your lucky day is later. Guess again (1~30):");
            }
        }
        else {
            if (user_guess > secret_day) {
                printf("Your guess is too late. Your lucky day is earlier.\n");
            }
            else {
                printf("Your guess is too early. Your lucky day is later.\n");
            }
            printf("No attempts left. Your lucky day in April is the %dth.\n", secret_day);
        }
    }
    return 0;
}