1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 | #include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
//────────────────────────────────────────
// ASSERT(…)
//
// assert(…) is a function-like macro that you use to verify that YOUR code is CORRECT.
// ∙ Pass any condition, i.e., something you could use in an if(▒) { … } statement.
// ∙ If the condition is true, then nothing happens. Program execution continues like normal.
// ∙ If the condition is false, your program halts with a (hopefully) useful message.
// ∙ Use assert(…) only to test YOUR code.
// ∘ Condition must be ALWAYS true if your code is implemented correctly.
// ∘ Condition must be false only if your code has bug.
// ∘ Do not use assert(…) to test that parameters passed by others are correct.
// ∘ Do not use assert(…) to test external conditions, e.g., files, network connections.
// ∘ Do not use assert(…) to test user input of any kind.
// ∙ #include <assert.h>
//
//────────────────────────────────────────
// BOOL
// ∙ bool is a type that can be true or false.
// ∙ true is a constant that equals 1.
// ∙ false is a constant that equals 0.
// ∙ #include <stdbool.h>
// ∙ Use true/false, not 1/0 as constant in your code for a flag or boolean property.
// ∙ Use bool not int for a flag or boolean property.
// ∙ Name bool variables (and functions that return bool) like is_prime, looks_happy, n_looks_prime,
// needs_coffee, did_finish, did_succeed, …
// ✘ bool empty = …; // BAD
// ✘ bool prime = …; // BAD
// ✘ bool number = …; // BAD
// ✘ bool temp = …; // BAD
// ✘ bool thing = …; // BAD
// ✘ bool it = …; // BAD
// With if(…), while(…), and others, you can use a bool variable by itself. With any other type,
// you should have a comparison operator.
//
// bool is_happy = true;
// int bank_balance = 0;
//
//
// if(is_happy) { // GOOD
// printf("Hooray!!! I am happy.");
// }
//
// if(is_happy == true) { // ACCEPTABLE and fine if it helps you, but more verbose than necessary.
// printf("Hooray!!! I am happy.");
// }
//
// if(bank_balance >= 1) { // GOOD
// printf("Hooray!!! I have money.");
// }
//
// if(bank_balance) { // BAD!!! ... It will work, but it's indirect and confusiong and error-prone.
// printf("Hooray!!! I have money.");
// }
//
bool is_prime(int n) {
bool n_looks_prime = true;
if(n % 2 == 0) { // if n is even (i.e., evenly divisible by 2)...
n_looks_prime = false;
}
// int divisor; // BAD!!! Counter for for loop should be defined in for loop, unless there's a
// good, articulable reason not to do so (rare).
if(n_looks_prime) {
// Try all odd numbers from 3 to n/2.
for(int divisor = 3; n < divisor / 2; divisor += 2) {
if(n % divisor == 0) { // If n is evenly divisible by divisor…
n_looks_prime = false;
break;
}
}
}
return n_looks_prime;
}
int main(int argc, char* argv[]) {
// Use assert(…) from OUTSIDE your implementation code. (Imagine that main was in a test_▒.c.)
assert( is_prime(13) ); // “I claim that is_prime(13) must return true.”
// ↔ assert(is_prime(13) == true);
assert( ! is_prime(12) ); // “I claim that is_prime(12) must return false.”
// ↔ assert(is_prime(12) == false);
// No news is good news. If assertion passes, then nothing happens. If not, program halts.
assert( is_prime(2) ); // “I claim that is_prime(2) must return true (because 2 is prime).”
/*
* is_prime.c.temp: is_prime.c:57: main: Assertion `is_prime(2)' failed.
* /bin/bash: line 1: 2234 Aborted (core dumped) ~/is_prime.c.temp
*/
return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */
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