avinashn
diff --git a/caesar_cipher.py b/caesar_cipher.py
@@ -0,0 +1,67 @@
+#This is a python program to decode and encode a caesar-cypher, given its key.
+
+#Function to encrypt a given string.
+def encrypt(k):                                                                         
+    n,i=0,0
+    l="abcdefghijklmnopqrstuvwxyz"
+    l=list(l)
+    b=[]
+    a=input("enter text to be encrypted: ")
+    a=list(a)
+    while(n<len(a)):
+        if a[n].lower() in l:
+            if a[n].isupper():
+                i=l.index(a[n].lower())
+                i=(i+k)%26
+                b.append(l[i].upper())
+                n+=1
+            else:
+                i=l.index(a[n])
+                i=(i+k)%26
+                b.append(l[i])
+                n+=1
+        else:
+            if(a[n]==' '):
+                b.append(' ')
+                n+=1
+    print("The encrypted text is: ","".join(b))
+
+#Function to decrypt an encrypted string.
+def decrypt(k):                          
+    n,i=0,0 
+    l="abcdefghijklmnopqrstuvwxyz"
+    l=list(l)
+    b=[]
+    a=input("Enter cipher to be decrypted: ")
+    a=list(a)
+    while(n<len(a)):
+        if a[n].lower() in l:
+            if a[n].isupper():
+                i=l.index(a[n].lower())
+                i=(i-k)%26
+                b.append(l[i].upper())
+                n+=1
+            else:
+                i=l.index(a[n])
+                i=(i-k)%26
+                b.append(l[i])
+                n+=1
+        else:
+            if(a[n]==' '):
+                b.append(' ')
+                n+=1
+    print("Cipher after decryption is: ","".join(b))
+
+
+#Main
+opt=int(input("1.encrypt   2.decrypt   0.exit"))
+while(opt!=0):
+    if(opt==1):
+        n=int(input("enter key"))
+        encrypt(n)
+    elif(opt==2):
+        n=int(input("enter key"))
+        decrypt(n)
+    else:
+        print("enter valid option")
+    opt=int(input("1.encrypt 2.decrypt 0.exit"))