Common mistakes with if, else-if, and else

cpsc120_common_if_mistakes.cc

// Gist https://gist.github.com/mshafae/0a21e4c9277838ed0c57e3e9b9ecd5a3
// Filename cpsc120_common_if_mistakes.cc
// CompileCommand clang++ -std=c++17 cpsc120_common_if_mistakes.cc
// Common mistakes with if, else-if, and else

// -- Start -- Turns off warnings - do not do this at home
#pragma clang diagnostic ignored "-Wtautological-constant-out-of-range-compare"
#pragma clang diagnostic ignored "-Wempty-body"
#pragma clang diagnostic ignored "-Wparentheses"
// -- End -- Turns off warnings - do not do this at home

#include <iostream>
#include <string>

int main(int argc, char const *argv[]) {
  int number{42};
  // The assignment operator (=) always is 'true'
  // The common mistake is to accidentally use = instead of == or !=.
  if (number = 17) {
    std::cout << "number should be 42 when it is really " << number << ".\n";
  } else {
    std::cout << "number should be 42 when it is really " << number << ".\n";
  }

  // We have a habit of putting semicolons at the end of everything. With
  // if statements it will cause the if statement to abort and not execute
  // the body of the condition.
  if (number == 99); {
    std::cout << "number is " << number << " but it appears to be 99.\n";
  }
  // If you try to put an else here it won't compile because of the semicolon.

  // If you want to do a range
  if (33 < number < 47) {
    std::cout << "number is " << number
              << " and it passes the test 33 < number < 47.\n";
  } else if (number == 17) {
    std::cout << "number is " << number
              << " and it passes the test number == 17.\n";
  } else {
    std::cout << "number is " << number
              << " and it failed the test 33 < number < 47 and the test number "
                 "== 17.\n";
  }
  return 0;
}