Using recursion, let the user put an input and find all combinations that add upto given number. In c++ and explain each line of code.

Write a C++ program using classes and recursion functions to convert a number in a given base (the user enters the base - from 2 to 9) to a decimal number. The algorithm states that each successive digit in the number is multiplied by the base raised to the power corresponding to its position in the number. The low-order digit is in position 0. We sum together all of these products to get the decimal value. For example, in binary – base 2, if we have the binary number 111001, we convert it to decimal as follows: 1x 25+1x 24+1x23+0x2²+0x 21+1x 2º=57 For a base 5 number, 14230: 1x54+4x53+2x52+3x51+0 x 50=1190 Validate your input. You should check for invalid digits and provide an informative error message to the user. This program requires you to use a recursive function for the conversion to decimal. Failure to do that will result in no points awarded.

Need some help with this c++ problem In order to compute a power of two, you can take the next-lower power and double it. For example, if you want to compute 211 and you know that 210 = 1024, then 211 = 2 × 1024 = 2048. Based on this observation, write a recursive function int pow2(int n) where n is the exponent. If the exponent is negative, return -1. int pow2(int n) {        ..... }

Answer in C++, and make it easy for me to copy and paste to recheck work.   The "odd/even factorial" of a positive integer n is represented as n!! and is defined non-recursively as: (n)(n-2)(n-4)...(4)(2) if n is even and is (n)(n-2)(n-4)...(5)(3) (1) if n is odd.   For example 7!! equals 7*5*3*1 or 105 and 6!! equals 6*4*2 or 48.   Come up with a recursive definition for n!! and use it to guide you to write a function definition for a function called oddevenfact that recursively calculates the odd/even factorial value of its single int parameter.   The value returned by oddevenfact is a long.