Is it possible to declare two variables of different types in a for loop

Question

Is it possible to declare two variables of different types in the initialization body of a for loop in C     For example   for int i 0 j 0       defines two integers  Can I define an int and a char in the initialization body  How would this be done

User · Answer

Not possible  but you can do   float f  int i  for  i   0 f   0 0  i  lt  5  i                  Or  explicitly limit the scope of f and i using additional brackets         float f       int i      for  i   0 f   0 0  i  lt  5  i

User · Answer

No - but technically there is a work-around  not that i d actually use it unless forced to    for struct   int a  char b    s     0   a      s a  lt  5     s a         std  cout  lt  lt  s a  lt  lt       lt  lt  s b  lt  lt  std  endl

User · Answer

I think best approach is xian s answer   but         Nested for loop  This approach is dirty  but can solve at all version   so  I often use it in macro functions   for int  int 0     make local variable          loopOnce true  loopOnce  true  loopOnce false       for char  char 0   char lt 3   char                     do anything with             int   char         Additional 1   It can also be used to declare local variables and initialize global variables   float globalFloat   for int localInt 0     decalre local variable            1     0       for globalFloat 2 f  localInt lt 3  localInt       initialize global variable                     do          Additional 2   Good example   with macro function    If best approach can t be used because it is a for-loop-macro    define for two decl  decl 1   decl 2  cond  incr    for  decl 1    1     0       for  decl 2   cond    incr         for two decl int i 0  char c 0  i lt 3  i                     your body with            i  c             If-statement trick  if  A  a nullptr   else     for         a is visible   If you want initialize to 0 or nullptr  you can use this trick   but I don t recommend this because of hard reading   and it seems like bug

User · Answer

Define a macro    define FOR  typeX x valueX   typeY y valueY   condition  increments  typeX x  typeY y  for x valueX y valueY condition increments   FOR int i 0   int f 0 0   i  lt  5  i                  Just remember  your variable scopes will not be within the for loop this way either

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Also you could use like below in C     int j 3  int i 2  for    i lt n  amp  amp  j lt n   j j 2  i i 2        your code

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C  17  Yes  You should use a structured binding declaration   The syntax has been supported in gcc and clang since gcc-7 and clang-4 0  clang live example   This allows us to unpack a tuple like so  for  auto  i  f  s    std  tuple 1  1 0  std  string  quot ab quot     i  lt  N    i  f    1 5                  The above will give you   int i set to 1 double f set to 1 0 std  string s set to  quot ab quot   Make sure to  include  lt tuple gt  for this kind of declaration  You can specify the exact types inside the tuple by typing them all out as I have with the std  string  if you want to name a type  For example  auto  vec  i32    std  tuple std  vector lt int gt  3  4  5   std  int32 t 12    A specific application of this is iterating over a map  getting the key and value  std  unordered map lt K  V gt  m                for  auto amp   key  value    m                 See a live example here  C  14  You can do the same as C  11  below  with the addition of type-based std  get  So instead of std  get lt 0 gt  t  in the below example  you can have std  get lt int gt  t    C  11  std  make pair allows you to do this  as well as std  make tuple for more than two objects  for  auto p   std  make pair 5  std  string  quot Hello World quot     p first  lt  10    p first        std  cout  lt  lt  p second  lt  lt  std  endl     std  make pair will return the two arguments in a std  pair   The elements can be accessed with  first and  second  For more than two objects  you ll need to use a std  tuple for  auto t   std  make tuple 0  std  string  quot Hello world quot    std  vector lt int gt              std  get lt 0 gt  t   lt  10            std  get lt 0 gt  t         std  cout  lt  lt  std  get lt 1 gt  t   lt  lt  std  endl     cout Hello world     std  get lt 2 gt  t  push back std  get lt 0 gt  t       add counter value to the vector    std  make tuple is a variadic template that will construct a tuple of any number of arguments  with some technical limitations of course    The elements can be accessed by index with std  get lt INDEX gt  tuple object  Within the for loop bodies you can easily alias the objects  though you still need to use  first or std  get for the for loop condition and update expression for  auto t   std  make tuple 0  std  string  quot Hello world quot    std  vector lt int gt              std  get lt 0 gt  t   lt  10            std  get lt 0 gt  t         auto amp  i   std  get lt 0 gt  t       auto amp  s   std  get lt 1 gt  t       auto amp  v   std  get lt 2 gt  t       std  cout  lt  lt  s  lt  lt  std  endl     cout Hello world     v push back i      add counter value to the vector     C  98 and C  03 You can explicitly name the types of a std  pair  There is no standard way to generalize this to more than two types though  for  std  pair lt int  std  string gt  p 5   quot Hello World quot    p first  lt  10    p first        std  cout  lt  lt  p second  lt  lt  std  endl

User · Answer

See   Is there a way to define variables of two types in for loop   for another way involving nesting multiple for loops  The advantage of the other way over Georg s  struct trick  is that it  1  allows you to have a mixture of static and non-static local variables and  2  it allows you to have non-copyable variables  The downside is that it is far less readable and may be less efficient

User · Answer

You can t declare multiple types in the initialization  but you can assign to multiple types E G        int i     char x     for i   0  x    p                            Just declare them in their own scope

[c++] Is it possible to declare two variables of different types in a for loop?

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