Initial commit.

.clang-format

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+BasedOnStyle: LLVM
+IndentWidth: 4
+ColumnLimit: 120
+AllowShortIfStatementsOnASingleLine: true

.gitignore

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+# Developer artifacts
+.cache/
+compile_commands.json
+
+# Compilation
+*.o
+quadratic

LICENSE.txt

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+MIT License
+
+Copyright (c) 2024 Matteo Golin
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Makefile

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+CC = gcc
+OUT = quadratic
+
+# Compilation warnings
+WARNINGS += -Wall -Wextra -Wshadow -Wundef -Wformat=2 -Wtrampolines -Wfloat-equal
+WARNINGS += -Wbad-function-cast -Wstrict-prototypes -Wpacked
+WARNINGS += -Wno-aggressive-loop-optimizations -Wmissing-prototypes -Winit-self
+WARNINGS += -Wmissing-declarations -Wmissing-format-attribute -Wunreachable-code
+WARNINGS += -Wshift-overflow=2 -Wduplicated-cond -Wpointer-arith -Wwrite-strings
+WARNINGS += -Wnested-externs -Wcast-align -Wredundant-decls
+WARNINGS += -Werror=implicit-function-declaration -Wlogical-not-parentheses
+WARNINGS += -Wlogical-op -Wold-style-definition -Wcast-qual -Wdouble-promotion
+WARNINGS += -Wunsuffixed-float-constants -Wmissing-include-dirs -Wnormalized
+WARNINGS += -Wdisabled-optimization -Wsuggest-attribute=const
+
+# Compilation flags
+CFLAGS = -O3 -lm
+
+# Source files
+SRCDIR = .
+SRCS = $(wildcard $(SRCDIR)/*.c)
+OBJS = $(patsubst %.c,%.o,$(SRCS))
+
+%.o: %.c
+	$(CC) $(CFLAGS) $(WARNINGS) -o $@ -c $<
+
+all: $(OBJS)
+	$(CC) $(CFLAGS) $^ -o $(OUT)
+
+clean:
+	@rm $(OBJS)

README.md

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+# quadratic
+
+A simple command line program for solving the quadratic equation. I built this purely to save me a little time when
+doing algebra for my engineering homework. The quadratic formula shows up quite often in circuit problems for non-linear
+circuits, and it becomes tedious to evaluate the quadratic formula each time.
+
+# Usage
+
+To see usage instructions for this program, please run `quadratic -h`.
+
+Example output:
+
+```console
+[user]$ quadratic -- 1 -10 16
+1.000000x^2 + -10.000000x + 16.000000
+x = 8.000000
+x = 2.000000
+
+[user]$ quadratic -v y -- 1 -10 16
+1.000000y^2 + 2.000000y + 3.000000
+x = -1.000000 + 1.414214i
+x = -1.000000 + -1.414214i
+
+```
+
+# Build/Installation
+
+The build recipe is in the Makefile. Running `make all` will create a binary called `quadratic` which you can then run.
+
+Although only tested on Linux, this program should build and run just fine on all other platforms.

main.c

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+#include <getopt.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/** Program version. */
+#define VERSION "0.0.0"
+
+/** Struct to represent a quadratic polynomial of format ax^2 + bx + c. */
+struct quadratic_t {
+    double a; /**< The a coefficient. */
+    double b; /**< The b coefficient. */
+    double c; /**< The c coefficient. */
+};
+
+/** Struct to represent a complex number. */
+struct complex_t {
+    double re; /**< The real component. */
+    double im; /**< The imaginary component. */
+};
+
+/** By default show the equation using the variable x. */
+static char variable = 'x';
+
+/** Check that the coefficient exists. */
+#define check_coeff(coeff)                                                                                             \
+    if (optind >= argc) {                                                                                              \
+        fprintf(stderr, "Missing coefficient '" coeff "'\n");                                                          \
+        print_usage();                                                                                                 \
+        exit(EXIT_FAILURE);                                                                                            \
+    }
+
+void print_usage(void);
+void print_complex(struct complex_t *c);
+void quadratic_formula(struct quadratic_t *poly, struct complex_t *z0, struct complex_t *z1);
+
+int main(int argc, char **argv) {
+
+    /* Parse options. */
+    int c;
+    while ((c = getopt(argc, argv, ":hv:")) != -1) {
+        switch (c) {
+        case 'h':
+            print_usage();
+            exit(EXIT_SUCCESS);
+        case 'v':
+            variable = optarg[0];
+            break;
+        case ':':
+            fprintf(stderr, "Option -%c requires an argument.\n", optopt);
+            print_usage();
+            exit(EXIT_FAILURE);
+        case '?':
+            fprintf(stderr, "Unknown option `-%c'.\n", optopt);
+            print_usage();
+            exit(EXIT_FAILURE);
+        default:
+            print_usage();
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    /* Parse all three coefficients. */
+    struct quadratic_t polynomial;
+
+    check_coeff("a");
+    polynomial.a = strtod(argv[optind], NULL);
+    optind++;
+
+    check_coeff("b");
+    polynomial.b = strtod(argv[optind], NULL);
+    optind++;
+
+    check_coeff("c");
+    polynomial.c = strtod(argv[optind], NULL);
+    optind++;
+
+    /** Plug coefficients into the quadratic formula and determine the zero. */
+    struct complex_t z0;
+    struct complex_t z1;
+    quadratic_formula(&polynomial, &z0, &z1);
+
+    /** Display results. */
+    printf("%lf%c^2 + %lf%c + %lf\n", polynomial.a, variable, polynomial.b, variable, polynomial.c);
+
+    // First zero
+    printf("x = ");
+    print_complex(&z0);
+    putchar('\n');
+
+    // Second zero
+    printf("x = ");
+    print_complex(&z1);
+    putchar('\n');
+
+    return EXIT_SUCCESS;
+}
+
+/**
+ * Performs the quadratic formula calculation to find two zeros for a polynomial.
+ * @param poly The polynomial to use for the calculation.
+ * @param z0 Where the first calculated zero of the polynomial will be stored.
+ * @param z1 Where the second calculated zero of the polynomial will be stored.
+ */
+void quadratic_formula(struct quadratic_t *poly, struct complex_t *z0, struct complex_t *z1) {
+
+    double discriminant = (poly->b * poly->b) - 4.0 * poly->a * poly->c;
+    double denominator = (2.0 * poly->a); // 2a term in denominator
+
+    // Non complex roots
+    if (discriminant >= 0.0) {
+        z0->re = (-poly->b + sqrt(discriminant)) / denominator;
+        z1->re = (-poly->b - sqrt(discriminant)) / denominator;
+        z0->im = 0.0;
+        z1->im = 0.0;
+        return;
+    }
+
+    // Both zeroes will have the same real component
+    z0->re = -poly->b / denominator;
+    z1->re = z0->re;
+
+    // Zeroes will have complementary imaginary components
+    z0->im = sqrt(-discriminant) / denominator;
+    z1->im = -z0->im;
+}
+
+/**
+ * Prints a complex number to stdout.
+ * @param c The complex number to print.
+ */
+void print_complex(struct complex_t *c) {
+
+    // Don't print the imaginary component if there is none
+    if (c->im == 0.0) {
+        printf("%lf", c->re);
+        return;
+    }
+
+    printf("%lf + %lfi", c->re, c->im);
+}
+
+/**
+ * Prints usage information about the command line program.
+ */
+void print_usage(void) {
+    puts("quadratic v" VERSION);
+    puts("MIT License | By Matteo Golin, 2024");
+    putchar('\n');
+    puts("DESCRIPTION:");
+    puts("\tFinds the zeroes of a quadratic polynomial in form ax^2 + bx + c.");
+    putchar('\n');
+    puts("USAGE:");
+    puts("\tquadratic [options] -- a b c");
+    puts("\tEnsure you include the '--' before the coefficients so negative numbers are properly parsed.");
+    putchar('\n');
+    puts("EXAMPLES:");
+    puts("\tquadratic -- 1 -10 16");
+    puts("\t1.000000x^2 + -10.000000x + 16.000000");
+    puts("\tx = 8.000000");
+    puts("\tx = 2.000000");
+    putchar('\n');
+    puts("\tquadratic -v y -- 1 -10 16");
+    puts("\t1.000000y^2 + 2.000000y + 3.000000");
+    puts("\tx = -1.000000 + 1.414214i");
+    puts("\tx = -1.000000 + -1.414214i");
+    putchar('\n');
+    puts("ARGUMENTS");
+    puts("\ta\tThe value of the a coefficient of the polynomial.");
+    puts("\tb\tThe value of the b coefficient of the polynomial.");
+    puts("\tc\tThe value of the c coefficient of the polynomial.");
+    putchar('\n');
+    puts("OPTIONS:");
+    puts("\tv\tThe variable to show as being solved for in the quadratic equation. Defaults to x.");
+    puts("\th\tPrints this help screen and exits.");
+}