1 files changed, 40 insertions, 0 deletions
diff --git a/25_break_encr/encryption.c b/25_break_encr/encryption.c
new file mode 100644
index 0000000..3e3b6b1
--- /dev/null
+++ b/25_break_encr/encryption.c
@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+
+void encrypt(FILE * f, int key) {    
+  int c;    
+  while ((c = fgetc(f)) != EOF) {        
+    if (isalpha(c)) {            
+      c = tolower(c);            
+      c -= 'a';            
+      c += key;            
+      c %= 26;            
+      c += 'a';        
+    }        
+    printf("%c", c);    
+  }
+}
+
+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;  
+  }  
+  encrypt(f,key);  
+  if (fclose(f) != 0) {    
+    perror("Failed to close the input file!");    
+    return EXIT_FAILURE;  
+  }  
+  return EXIT_SUCCESS;
+}