Problems:

CS100 Homework 1 (Spring 2023)#

Deadline: 2023-02-26 (Sun) 23:59:59

Late submission will open for 24 hours after the deadline, with 50% point deduction.

If you get full marks in this assignment by no more than 20 submission attempts, you can earn special OJ displays and a “1-case protection” that can be used in further assignments to cancel one testcase failure. See Piazza or OJ dashboard for more information.

Problem 1: Find Bugs!#

Description#

Your friend has just started learning programming, and has spent hours on a textbook practice problem. He/She asks you for help by treating you to a KFC Crazy Thursday meal. You agree, and he/she sends you a .txt file:

#include <sudo.h>

void main（）
{
    // Calculate the average score of all students in a class.

    int num;
    int sum;

    printf('How many students are there?/n')
    scanf('d%', num)
    printf("What are their scores?/n")

    // We programmers count from zero!
    for (int i = 0, i <= num, i++);
    {
        int sum, score;
        scanf("d%", score);
        sum += score;
    }

    double average = sum / num;
    if (average = 60)
        printf('Good!/n');
    if (average > 60)
        printf('Excellent!/n');
    else
        printf(“Bad!/n”);

    printf("Average score is &.2f./n", average);

    return 0;
}

For the sake of Crazy Thursday, you now have the responsibility to debug your friend’s code (Don’t do so in ShanghaiTech!). You may first fix compile errors so that the code runs, and then figure out why it (possibly) does not produce correct results.

Input format#

The first line contains a number , representing the number of students in a class.

The following lines each contain , score of a student.

For 100% cases, $0 < n \leqslant 50$ , and $0 < s_i \leqslant 100$ .

Output format#

Four sentences, specified as in printf statements in the code.

In the last sentence, format the average score to 2 decimal digits.

Example#

Input:

2
70
81

Output:

How many students are there?
What are their scores?
Excellent!
Average score is 75.50.

Test cases#

👉 Go to GitHub

Problem 2: Equation of A Line#

Description#

Input two points’ coordinates $(x,\ y)$ , where $x$ and $y$ are two integers. You need to calculate the equation of the line going through these two points in the form of $y = kx + b$ , or $x = c$ (when the slope k doesn’t exist).

Input format#

Two lines, each containing a coordinate in the form (x, y) , where x and y are integers.

For 100% cases, $|x| < 1000$ , and $|y| < 1000$ .

Output format#

A line in the form of y = kx [+/-] b , or x = c .

k , b and c should all be of type double . When printed, format them to 2 decimal digits. If b < 0 , the minus sign - should take place of the + , turning the result into y = kx - b .
You do not need to simplify the cases $b= 0$ , $k=0$ , and $k = \pm 1$ . Just leave the number there, like y = 1.00x + 0.00.

Pay attention to spaces before and after '=' and '+'/'-' . It’s safest to directly copy-paste the above equations into your code.

Example#

Input:

(2, -1)
(4, -3)

Output:

y = -1.00x + 1

Input:

(-2, 3)
(4, -6)

Output:

y = -1.50x + 0

Input:

(-10, -3)
(2, -3)

Output:

y = 0.00x - 3

Input:

(-2, 0)
(-2, 1)

Output:

x = -2

Test cases#

👉 Go to GitHub

Problem 3: Spell It Out#

Description#

“How I wish that numbers could be gone!”, cursed you after a terrible math exam. That exact night, you had a bad dream where all numbers have disappeared! No one understands 1, 2, 3, and you had to spell them out in English like one, two, three!

Luckily you had a computer to do all this, and a piece of guide to follow:

Use a hyphen ('-') to connect a word ending in -ty to another word. (22 -> twenty-two, 48000 -> forty-eight thousand)
There is NO “-s” (plural) for words “hundred” and “thousand”. Also, 100 and 1000 are spelled “one hundred” and “one thousand”.
To use or to not use an “and” after “hundred” is both OK. However, inserting an “and” makes the spelling easier to read, so let’s put an “and” after “hundred” or “thousand” when they are followed by a part less than 100. (101 -> one hundred and one, 2023 -> two thousand and twenty-three, 114500 -> one hundred and fourteen thousand five hundred)
NO comma (',') after the world “thousand”, although it sounds more natural to stop there when reading numbers out.
Pay attention to spellings, especially for “fourteen”, “forty”, “nineteen”, and “ninety”! You don’t want to spend hours debugging to find out nothing but a typo!

Input description#

The input is a number.

For 20% cases, $0 \leqslant x \leqslant 999$ .
For 20% cases, x % 1000 == 0 .
For 100% cases, $0 \leqslant x \leqslant 999999$ .

Output description#

You should output the English spelling of number x in one line. It’s OK whether you end the line with a '\n' or not.

Hints#

This problem does NOT involve strings (something we haven’t learned)! Try to separate the output into different parts, and print each one with a printf! Keep in mind that printf does not necessarily end with a '\n' .
Some work might need to be performed multiple times (like translating 1-9 into “one” through “nine”). Why not write them into functions to make things easy and avoid bugs?

Sample input/outputs#

Input	Output
0	zero
44	forty-four
1590	one thousand five hundred and ninety
114500	one hundred and fourteen thousand five hundred

Appendix: Numbers in English#

0	1	2	3	4	5	6	7	8	9
zero	one	two	three	four	five	six	seven	eight	nine

10	11	12	13	14	15	16	17	18	19
ten	eleven	twelve	thirteen	fourteen	fifteen	sixteen	seventeen	eighteen	nineteen

20	30	40	50	60	70	80	90	100	1000
twenty	thirty	forty	fifty	sixty	seventy	eighty	ninety	hundred	thousand

Test cases#

👉 Go to GitHub

Reference solutions#

Remember, you should always solve all the problems yourself and passed all the testcases first.