Initial commit

01.c

+#include <stdio.h>
+
+int main() {
+    int c = 'X';
+    fread(c, sizeof(char), 1, stdin);
+    printf("I got: %c\n", c);
+}

02.c

+#include <stdio.h>
+
+int main() {
+    int c = 'X';
+    fread(&c, sizeof(char), 1, stdin);
+    printf("I got: %c\n", c);
+}

bases.c

+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <errno.h>
+
+const char HEX_DIGITS[] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
+
+static inline int to_nibble(char *bin) {
+    char *endptr = NULL;
+    char *dup = strndup(bin, 4);
+    int result = strtol(dup, &endptr, 2);
+    if (dup + strlen(dup) != endptr) {
+        free(dup);
+        return -1;
+    }
+    free(dup);
+    return result; 
+}
+
+char *pad_to_n(char *str, size_t n) {
+    size_t len = (strlen(str) / n + 1) * n;
+    char *out = calloc(len + 1, sizeof(char));
+    char *ptr = out;
+    for (size_t i = 0; i < len - strlen(str); i++) {
+        *ptr = '0';
+        ptr++;
+    }
+    while (*str) {
+        *ptr = *str;
+        ptr++;
+        str++;
+    }
+    return out;
+}
+
+char *bin_to_hex(char *num) {
+    char *padded = pad_to_n(num, 8);
+    char *ptr = padded; 
+    char *end = padded + strlen(padded);
+    char *out = calloc(strlen(padded) / 4 + 1, sizeof(char));
+
+    size_t i = 0;
+    while (ptr < end) {
+        int num = to_nibble(ptr);
+        if (num == -1) {
+            free(padded);
+            free(out);
+            return NULL;
+        }
+        out[i] = HEX_DIGITS[num];
+        ptr += 4;
+        i++;
+    }
+    free(padded);
+    return out;
+}

main.c

+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+char *readline(char **buf);
+char *bin_to_hex(char *num);
+
+static int strip_leading_zeroes(char **ptr) {
+    int result = 0;
+    while ((*ptr)[0] == '0' && (*ptr)[1] != '\0') {
+        (*ptr)++;
+        result++;
+    }
+    return result;
+}
+
+static inline void test_case(char *num) {
+    char *hex = bin_to_hex(num);
+    if (!hex) {
+        printf("Invalid input.\n");
+        return;
+    }
+    int leading_zeroes = strip_leading_zeroes(&hex);
+    printf("hex(0b%s) = 0x%s\n", num, hex);
+    free(hex - leading_zeroes);
+}
+
+int main(int argc, char **argv) {
+    char *buf = calloc(10000, 1);
+    while (true) {
+        printf("Enter a binary number to convert: ");
+        char *line = readline(&buf);
+        if (strlen(line) && strcmp(line, "exit") != 0) {
+            test_case(line);
+        }
+        else {
+            break;
+        }
+    }
+}

readline.c

+#include <stdio.h>
+
+char *readline(char **buf) {
+    int charsread = 0;
+    char c = '\n';
+    while (fread(&c, sizeof(char), 1, stdin) && c != '\n') {
+        charsread++;
+        **buf = c;
+        (*buf) += 1;
+    }
+    return (*buf) - charsread;
+}