Brainlag
  1. C
  2. Foundations
07/38

Checkpoint: the foundations

Checkpoint25 min4 problems
  1. 1Before the memory lessons
  2. 2Season stats from input
  3. 3Damage on an unsigned byte
  4. 4Nine evens out of twenty
  5. 5Battle pass tiers

Learn

Before the memory lessons

Four problems that use everything so far: printf, scanf, types, division, if and loops, functions and bits. No starter scaffolding beyond what a real task gives you, and no hints until your first check. Next up is where values actually live in memory, so this is a good moment to find out what has stuck.

Checkpoint

Season stats from input

The input is a count n, then n scores. Print one line: how many scores, their total, the average to one decimal place and the best score. Check runs three different inputs, including one where every score is negative.

For 4 then 10 20 35 41 the line is count 4, total 106, average 26.5, best 41.

Milestones

  1. Four scores
  2. All negative
  3. Just one

On your own: hints appear after your first check, a solution after 3 checks or if you give up.

Your program reads the Input box under the editor. Check also tries 2 other inputs.

exercise_1.c to run
#include <stdio.h>

int main(void) {
    int n;
    scanf("%d", &n);

    return 0;
}

CheckpointPredict the output

Damage on an unsigned byte

A character's health is stored in an unsigned char. Type exactly what this prints.

Read the program, type exactly what it prints, then lock it in. It runs after that.

exercise_2.c
#include <stdio.h>

int main(void) {
    unsigned char hp = 3;
    hp = hp - 5;
    printf("%u\n", hp);
    printf("%x\n", hp);
    printf("%d\n", 9 / 4 * 4);
    printf("%d\n", (5 >> 1) & 1);
    return 0;
}

CheckpointFix the bug

Nine evens out of twenty

This should count the even numbers from 1 to 20 inclusive and print 10 even numbers from 1 to 20. It has two problems. Fix both.

On your own: hints appear after your first check, a solution after 3 checks or if you give up.

exercise_3.c to run
#include <stdio.h>

int main(void) {
    int count = 0;
    for (int i = 1; i < 20; i++) {
        if (i % 2 == 0) count++
    }
    printf("%d even numbers from 1 to 20\n", count);
    return 0;
}

Checkpoint

Battle pass tiers

A battle pass starts at tier 1 with 0 XP. Each tier costs 100 XP more than the one before: tier 2 needs 100 XP in total, tier 3 needs 300 (100 + 200), tier 4 needs 600 (300 + 300), and so on with no top tier. Write two functions, for any xp of 0 or more:

  • int tier_for(int xp) returns the tier reached with that much XP.
  • int xp_to_next(int xp) returns how much more XP the next tier needs.

On your own: hints appear after your first check, a solution after 3 checks or if you give up.

exercise_4.c to run

  
  

  

  





    
    

    

    
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C, 32-bit: int and pointers are 4 bytes