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1 files changed, 60 insertions, 0 deletions

diff --git a/28_fix_vg_encr/encrypt.c b/28_fix_vg_encr/encrypt.c
new file mode 100644
index 0000000..71b7156
--- /dev/null
+++ b/28_fix_vg_encr/encrypt.c
@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <string.h>
+
+void encrypt(FILE * f, int key, FILE * outfile){
+  char * line=NULL;
+  size_t sz=0;
+  while (getline(&line,&sz, f) >= 0) {
+    char * ptr = line;
+    while (*ptr != '\0') {
+      int c = *ptr;
+      if (isalpha(c)) {
+        c = tolower(c);
+        c -= 'a';
+        c += key;
+        c %= 26;
+        c += 'a';
+      }
+      *ptr = c;
+      ptr++;
+    }
+    fprintf(outfile, "%s", line);
+  }
+  free(line);
+}
+
+int main(int argc, char ** argv) {
+  if (argc != 3) {
+    fprintf(stderr,"Usage: encrypt key inputFileName\n");
+    return EXIT_FAILURE;
+  }
+  int key = atoi(argv[1]);
+  if (key == 0) {
+    fprintf(stderr,"Invalid key (%s): must be a non-zero integer\n", argv[1]);
+    return EXIT_FAILURE;
+  }
+  FILE * f = fopen(argv[2], "r");
+  if (f == NULL) {
+    perror("Could not open file");
+    return EXIT_FAILURE;
+  }
+  //outfileNAme is argv[2] + ".txt", so add 4 to its length.
+  char * outFileName = malloc((strlen(argv[2]) + 5) * sizeof(*outFileName));
+  strcpy(outFileName, argv[2]);
+  strcat(outFileName, ".enc");
+  FILE * outFile = fopen(outFileName, "w");
+  encrypt(f,key, outFile);
+  if (fclose(outFile) != 0) {
+    perror("Failed to close the input file!");
+    return EXIT_FAILURE;
+  }
+  if (fclose(f) != 0) {
+    perror("Failed to close the input file!");
+    return EXIT_FAILURE;
+  }
+  free(outFileName);
+
+  return EXIT_SUCCESS;
+}