feat(solutions): add convert-number-from-base-to-another/c/function

challenges/convert-number-from-base-to-another/solutions/c/function/README.md

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+# convert-number-from-base-to-another/c/function
+
+Created by [@Divlo](https://github.com/Divlo) on 20 October 2021.

challenges/convert-number-from-base-to-another/solutions/c/function/character.c

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+#include "character.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+void character_append(char* string, char character) {
+  size_t length = strlen(string);
+  string[length] = character;
+  string[length + 1] = '\0';
+}

challenges/convert-number-from-base-to-another/solutions/c/function/character.h

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+#ifndef __CHARACTER__
+#define __CHARACTER__
+
+/**
+ * @brief Append a character to a string, assuming string points to an array
+ * with enough space.
+ *
+ * @param string
+ * @param character
+ */
+void character_append(char* string, char character);
+
+#endif

challenges/convert-number-from-base-to-another/solutions/c/function/input.c

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+#include "input.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "character.h"
+
+char* input() {
+  char character;
+  size_t length = 1;
+  char* string = malloc(length * sizeof(char));
+  *string = '\0';
+  while ((character = getchar()) != '\n' && character != EOF) {
+    length++;
+    string = realloc(string, length * sizeof(char));
+    character_append(string, character);
+  }
+  return string;
+}

challenges/convert-number-from-base-to-another/solutions/c/function/input.h

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+#ifndef __INPUT__
+#define __INPUT__
+
+/**
+ * @brief Read a line from stdin.
+ *
+ * @return char*
+ */
+char* input();
+
+#endif

challenges/convert-number-from-base-to-another/solutions/c/function/solution.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "input.h"
+
+int math_power(int base, int power) {
+  int result = 1;
+  for (int iteration = 0; iteration < power; iteration++) {
+    result = result * base;
+  }
+  return result;
+}
+
+char* convert_from_base_10_to_base(unsigned long number, unsigned int base) {
+  if (number == 0) {
+    return "0";
+  }
+  int remainders[64] = {};
+  int index = 0;
+  while (number > 0) {
+    remainders[index] = number % base;
+    number = number / base;
+    index++;
+  }
+  char* result = malloc(sizeof(char) * (index + 1));
+  int index_result = 0;
+  for (int iteration = index - 1; iteration >= 0; iteration--) {
+    int remainder = remainders[iteration];
+    if (remainder >= 10) {
+      result[index_result] = (char)((remainder - 10) + 'A');
+    } else {
+      result[index_result] = (char)(remainder + '0');
+    }
+    index_result++;
+  }
+  return result;
+}
+
+int convert_from_base_to_base_10(char* number, unsigned int base) {
+  int length = strlen(number);
+  int exponent = length - 1;
+  int result = 0;
+  int index = 0;
+  while (exponent >= 0) {
+    int current_number = (int)(number[index] - '0');
+    if (current_number >= 10) {
+      current_number = (int)(number[index] - 'A') + 10;
+    } else {
+      current_number = (int)(number[index] - '0');
+    }
+    result = result + current_number * math_power(base, exponent);
+    exponent--;
+    index++;
+  }
+  return result;
+}
+
+int main() {
+  char* number = input();
+  int base_from;
+  int base_target;
+  scanf("%d", &base_from);
+  scanf("%d", &base_target);
+  printf("%s\n", convert_from_base_10_to_base(convert_from_base_to_base_10(number, base_from), base_target));
+  return EXIT_SUCCESS;
+}