Renaming digressions to gnu-c

since that better describes what I'm doing in there, plus removed the
silly java prog because it was silly and not GNU C.

gnu-c/.gitignore

@@ -0,0 +1,3 @@
+/temperatures
+/qsort-example
+/getopt-example

gnu-c/Makefile

@@ -0,0 +1,6 @@
+TARGETS := $(patsubst %.c,%,$(wildcard *.c))
+CFLAGS += -g -Wall -Wextra -pedantic -pedantic-errors
+
+all: $(TARGETS)
+
+.PHONY: all

gnu-c/getopt-example.c

@@ -0,0 +1,54 @@
+/*
+ * Example getopt usage mostly from getopt(3)
+ */
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <libgen.h>
+
+
+void die_usage(char *prog, char *msg) {
+    fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n", prog);
+    if (msg != NULL) {
+        fprintf(stderr, "%s\n", msg);
+    }
+    exit(EXIT_FAILURE);
+}
+
+
+int main(int argc, char *argv[]) {
+    char *prog;
+    int flags, opt;
+    int nsecs, tfnd;
+
+    nsecs = 0;
+    tfnd = 0;
+    flags = 0;
+    prog = basename(argv[0]);
+
+    while ((opt = getopt(argc, argv, "hnt:")) != -1) {
+        switch (opt) {
+        case 'n':
+            flags = 1;
+            break;
+        case 't':
+            nsecs = atoi(optarg);
+            tfnd = 1;
+            break;
+        case 'h':
+        default: /* '?' */
+            die_usage(prog, NULL);
+        }
+    }
+
+    printf("flags=%d; tfnd=%d; optind=%d\n", flags, tfnd, optind);
+
+    if (optind >= argc) {
+        die_usage(prog, "Expected argument after options");
+    }
+
+    printf("name argument = %s\n", argv[optind]);
+    printf("nsecs = %d\n", nsecs);
+
+    exit(EXIT_SUCCESS);
+}

gnu-c/qsort-example.c

@@ -0,0 +1,34 @@
+/*
+ * C Sorting example mostly from qsort(3)
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <libgen.h>
+
+
+static int cmpstringp(const void *p1, const void *p2) {
+    /* The actual arguments to this function are "pointers to
+       pointers to char", but strcmp(3) arguments are "pointers
+       to char", hence the following cast plus dereference */
+
+    return strcmp(*(char * const *)p1, *(char * const *)p2);
+}
+
+
+int main(int argc, char *argv[]) {
+    int j;
+
+    if (argc < 2) {
+        fprintf(stderr, "Usage: %s <string>...\n", basename(argv[0]));
+        exit(EXIT_FAILURE);
+    }
+
+    qsort(&argv[1], argc - 1, sizeof(argv[1]), cmpstringp);
+
+    for (j = 1; j < argc; j++) {
+        puts(argv[j]);
+    }
+
+    exit(EXIT_SUCCESS);
+}

gnu-c/temperatures.c

@@ -0,0 +1,73 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <libgen.h>
+
+
+double c2f(double celsius) {
+    return ((9.0 / 5.0) * celsius) + 32.0;
+}
+
+
+double f2c(double fahrenheit) {
+    return (5.0 / 9.0) * (fahrenheit - 32.0);
+}
+
+
+void usage(const char *prog, const char *msg) {
+    fprintf(stderr, "Usage: %s <temp>[fFcC]\n", prog);
+    if (msg != NULL) {
+        fprintf(stderr, "%s\n", msg);
+    }
+}
+
+
+int main(int argc, char * argv[]) {
+    const char * prog = basename(argv[0]);
+    int ret;
+    char msg[255];
+    double temp;
+    char scale = '\0';
+    const char *in_fmt = "%lf%c";
+    const char *out_fmt = "%.2lf%c\n";
+    const char *temp_string;
+
+    if (argc < 2) {
+        usage(prog, NULL);
+        exit(EXIT_FAILURE);
+    }
+
+    if (((int)strlen(argv[1]) == 1) && (argv[1][0] == '-')) {
+        ret = fscanf(stdin, in_fmt, &temp, &scale);
+    } else {
+        temp_string = argv[1];
+        ret = sscanf(temp_string, in_fmt, &temp, &scale);
+    }
+
+    if ((ret == 0) || (ret == EOF)) {
+        usage(prog, "No temperature provided!");
+        exit(EXIT_FAILURE);
+    }
+
+    if (ret == 1) {
+        usage(prog, "No scale provided!");
+        exit(EXIT_FAILURE);
+    }
+
+    switch (scale) {
+        case 'c':
+        case 'C':
+            printf(out_fmt, c2f(temp), 'F');
+            break;
+        case 'f':
+        case 'F':
+            printf(out_fmt, f2c(temp), 'C');
+            break;
+        default:
+            sprintf(msg, "Unknown scale: '%c'", scale);
+            usage(prog, msg);
+            break;
+    }
+
+    exit(EXIT_SUCCESS);
+}