Solve challenge 5

ex05/input.txt

@@ -0,0 +1,2 @@
+Burning 'em, if you ain't quick and nimble
+I go crazy when I hear a cymbal

ex05/main.c

@@ -0,0 +1,41 @@
+#include "utils.h"
+#include <ctype.h>
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char *argv[]) {
+  if (argc < 3) {
+    printf("Usage: %s <key> <filename>\n", argv[0]);
+    return EXIT_FAILURE;
+  }
+
+  const char *key = argv[1];
+  const char *filename = argv[2];
+
+  FILE *fp = fopen(filename, "r");
+  if (fp == NULL) {
+    printf("Error opening file %s\n", filename);
+    return EXIT_FAILURE;
+  }
+
+  unsigned int key_length = strlen(key);
+
+  char buf[1024];
+  size_t nread = 0;
+  size_t counter = 0;
+  while ((nread = fread(buf, 1, sizeof buf, fp)) > 0) {
+    for (size_t i = 0; i < nread; ++i) {
+      printf("%02x", buf[i] ^ key[counter % key_length]);
+      counter++;
+    }
+  }
+
+  putchar('\n');
+
+  if (fclose(fp)) {
+    printf("Error closing file %s\n", filename);
+    return EXIT_FAILURE;
+  }
+
+  return EXIT_SUCCESS;
+}

meson.build

@@ -7,3 +7,4 @@ executable('ex01', ['ex01/main.c', 'utils.c'], dependencies: m_dep)
 executable('ex02', ['ex02/main.c', 'utils.c'], dependencies: m_dep)
 executable('ex03', ['ex03/main.c', 'utils.c'], dependencies: m_dep)
 executable('ex04', ['ex04/main.c', 'utils.c'], dependencies: m_dep)
+executable('ex05', ['ex05/main.c', 'utils.c'], dependencies: m_dep)