Added typedef vs define file

Author: Priyankcoder

typedef vs define.cpp

@@ -0,0 +1,78 @@
+Typedef versus #define in C++
+
+typedef: The typedef is used to give data type a new name. For example,
+
+COde:
+
+// C program to demonstrate typedef 
+#include <stdio.h> 
+
+// After this line BYTE can be used 
+// in place of unsigned char 
+typedef unsigned char BYTE; 
+
+int main() 
+{ 
+	BYTE b1, b2; 
+	b1 = 'c'; 
+	printf("%c ", b1); 
+	return 0; 
+} 
+
+Output: c
+
+Code:
+
+// C program to demonstrate #define 
+#include <stdio.h> 
+
+// After this line HYD is replaced by 
+// "Hyderabad" 
+#define HYD "Hyderabad" 
+
+int main() 
+{ 
+	printf("%s ", HYD); 
+	return 0; 
+} 
+
+
+Output:
+Hyderabad
+
+
+Difference between typedef and #define:
+
+1.typedef is limited to giving symbolic names to types only, whereas #define can be used to define an alias for values as well, e.g., 2.you can define 1 as ONE, 3.14 as PI, etc.
+3.typedef interpretation is performed by the compiler where #define statements are performed by preprocessor.
+4.#define should not be terminated with a semicolon, but typedef should be terminated with semicolon.
+5.#define will just copy-paste the definition values at the point of use, while typedef is the actual definition of a new type.
+6.typedef follows the scope rule which means if a new type is defined in a scope (inside a function), then the new type name will only 7.be visible till the scope is there. In case of #define, when preprocessor encounters #define, it replaces all the occurrences, after 8.that (No scope rule is followed).
+
+
+typedef char* ptr;
+ptr a, b, c;
+
+the statement effectively becomes
+
+char *a, *b, *c;
+
+This declares a, b, c as char*.
+
+In contrast, #define works like this:
+
+#define PTR char*
+PTR x, y, z;
+
+the statement effectively becomes
+char *x, y, z;
+
+This makes x, y and z different, as, x is pointer-to-a char, whereas, y and z are char variables.
+
+
+Conclusion:
+
+Use typedef to give data type a new name and use #define to define constant and other alias.
+
+
+