Print 1 to 100 in C++, without loop and recursion
Following is a C++ program that prints 1 to 100 without loop and without recursion.
1 2 3 .. .. 98 99 100
The program prints all numbers from 1 to n without using a loop and recursion. The concept used in this program is Template Metaprogramming.
Let us see how this works. Templates in C++ allow non-datatypes also as parameter. Non-datatype means a value, not a datatype. For example, in the above program, N is passed as a value which is not a datatype. A new instance of a generic class is created for every parameter and these classes are created at compile time. In the above program, when compiler sees the statement “PrintOneToN<>::print()” with N = 100, it creates an instance PrintOneToN<100>. In function PrintOneToN<100>::print(), another function PrintOneToN<99>::print() is called, therefore an instance PrintOneToN<99> is created. Similarly, all instances from PrintOneToN<100> to PrintOneToN<2> are created. PrintOneToN<1>::print() is already there and prints 1. The function PrintOneToN<2> prints 2 and so on. Therefore we get all numbers from 1 to N printed on the screen.
Following is another approach to print 1 to 100 without loop and recursion.
The output of this program is same as above program. In the above program, class A has a static variable ‘a’, which is incremented with every instance of A. The default constructor of class A prints the value of ‘a’. When we create an array of objects of type A, the default constructor is called for all objects one by one. Therefore, we get all values from 1 to 100 printed on the screen.
Following is light weight approach to print 1 to 100 without loop and recursion with the use of goto keyword.
The output of this program is same as above program. In the above program, goto keyword is jump again to the label named update. Value of ‘sum’ is printed and incremented with every call. The program stop executing once the variable sum is equal to 100. In this way, we get all values from 1 to 100 printed on the console.
Thanks to Lakshmanan for suggesting this approach.
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