C++ automatic type promotion

Table of contents

Introduction

As mentioned at [C++ numerical

#define print_type(var) \
  fmt::print("{} = {} is {} \n", #var, var, typeid(var).name());

int main([[maybe_unused]] int argc, [[maybe_unused]] char **argv) {
  int a = 10;
  int b = 20;

  auto max1 = (a > b) ? a : b;      // max1 is i
  auto max2 = (a > b) ? 10.0f : b;  // max2 is f
  auto max3 = (a > b) ? a : 20.0f;  // max3 is f
  auto max4 = (a > b) ? 10.0 : b;   // max4 is d
  auto max5 = (a > b) ? a : 20.0;   // max5 is d

  short int x = 10;
  short int y = 20;
  short int z = 0;
  auto max6 = (x > y) ? x : y;  // max6 is s
  // 🔴 Implicit conversion to int
  // short int don't support arithmetic
  auto max7 = (x > y) ? x + z : y + z;  // max7 is i

  print_type(max1);
  print_type(max2);
  print_type(max3);
  print_type(max4);
  print_type(max5);
  print_type(max6);
  print_type(max7);
  return 0;
}

Possible output

max1 = 20 is i 
max2 = 20 is f 
max3 = 20 is f 
max4 = 20 is d 
max5 = 20 is d 
max6 = 20 is s 
max7 = 20 is i 

References

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