unsigned-integer

int main() { unsigned i = 5; int j = -10; double d = i + j; long l = i + j; int k = i + j; std::cout << d << "\n"; //4.29497e+09 std::cout << l << "\n"; //4294967291 std::cout << k << "\n"; //-5 std::cout << i + j << "\n"; //4294967291 } I believe signed int is promoted to unsigned before doing the arithmetic operators. While -10 is converted to unsigned unsigned integer underflow ( is this the correct term?? ) will occur and after addition it prints 4294967291 . Why this is not happening in the case of int k which print -5 ? The process of doing the arithmetic operator involves a conversion

Consider the following † : size_t r = 0; r--; const bool result = (r == -1); Does the comparison whose result initialises result have well-defined behaviour? And is its result true , as I'd expect? This Q&A was written because I was unsure of two factors in particular. They may both be identified by use of the term "crucial[ly]" in my answer. † This example is inspired by an approach for loop conditions when the counter is unsigned: for (size_t r = m.size() - 1; r != -1; r--) size_t r = 0; r--; const bool result = (r == -1); Strictly speaking, the value of result is implementation-defined. In

I tried: #include <vector> int main () { std::vector<int> v; int size = v.size; } but got the error: cannot convert 'std::vector<int>::size' from type 'std::vector<int>::size_type (std::vector<int>::)() const noexcept' {aka 'long unsigned int (std::vector<int>::)() const noexcept'} to type 'int' Casting the expression to int like this: #include <vector> int main () { std::vector<int> v; int size = (int)v.size; } also yields an error: error: invalid use of member function 'std::vector<_Tp, _Alloc>::size_type std::vector<_Tp, _Alloc>::size() const [with _Tp = int; _Alloc = std::allocator<int>;

I have made some research on Stackoverflow about reverse for loops in C++ that use an unsigned integer instead of a signed one. But I still do NOT understand why there is a problem (see Unsigned int reverse iteration with for loops ). Why the following code will yield a segmentation fault? #include <vector> #include <iostream> using namespace std; int main(void) { vector<double> x(10); for (unsigned int i = 9; i >= 0; i--) { cout << "i= " << i << endl; x[i] = 1.0; } cout << "x0= " << x[0] << endl; return 0; } I understand that the problem is when the index i will be equal to zero, because