Create caesar.c

Author: PhucNguyen12

pset2/caesar.c

@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <cs50.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+
+int main(int argc, string argv[])
+{
+    //Check key in command line argument
+   if(argc < 2 || argc > 2)
+   {
+        printf("Usage: must include a key\n");
+        return 1;
+   }
+   
+   //Get the key
+   int k = atoi(argv[1]);
+   
+   //Check the key
+   if ( k < 0)
+   {
+    printf("Key must be non-negative\n");
+    return 1;
+   }
+   
+   
+   //Declare some variables
+   string input = NULL;
+   string uppercaseAlpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+   string lowercaseAlpha = "abcdefghijklmnopqrstuvwxyz";
+   
+   //Ask user for plain text
+   do
+   {
+    input = GetString();
+   }while(input == NULL);
+   
+   //Print out the cipher text
+   for (int i = 0, n = strlen(input); i < n; i++)
+   {
+        if(!isalpha(input[i])) continue;
+        
+        char ci = input[i];
+        
+        if(isupper(ci))
+        {
+            int offset = ci + k - 'A';
+            offset = offset % 26;
+            ci = uppercaseAlpha[offset];
+            input[i] = ci;
+        }
+           
+        else if (islower(ci))
+        {
+            int offset = ci + k - 'a';
+            offset = offset % 26;
+            ci = lowercaseAlpha[offset];
+            input[i] = ci;
+        }
+   }
+   
+   printf("%s\n", input);
+    return 0;
+}