# References and Lambdas

In this chapter, we will work with references (both constant and
mutable) and also look at the basics of higher-order functions in
C++.

Demonstrations:

 1. ‹stats›      – input and output parameters
 2. ‹primes›     – fill in a vector with prime numbers
 3. ‹iterate›    – building sequences by iterating a function
 4. ‹newton›     – a general routine for numeric approximation

Elementary exercises:

 1. ‹fibonacci›  – old sequence, new function signature
 2. ‹normalize›  – divide out the gcd from a fraction
 3. ‹accumulate› – sum up ⟦f(x)⟧ for all ⟦x⟧ in an ‹std::vector›

Preparatory exercises:

 1. ‹rewrap›     – word wrapping redux, this time in-place
 2. ‹golden›     – basic uses of output parameters
 3. ‹divisors›   – collections as in/out parameters
 4. ‹midpoints›  – in/out parameters of custom types
 5. ‹higher›     – higher-order function primer: ‹map› and ‹zip›
 6. ‹fixpoint›   – find a fixed point of a monotonic function

Regular exercises:

 1. ‹euler›      – implement Euler's totient function ⟦φ⟧
 2. ‹approx›     – somewhat easier approximation
 3. ‹solve›      – a very simple game solver
 4. ‹sort›       – selection sort with a comparator
 5. ‹permute›    – compute a vector of digit permutations
 6. ‹bsearch›    – binary search with a comparator