Evaluate a string with a switch in C

Question

I want to evaluate a string with a switch but when I read the string entered by the user throws me the following error    include lt iostream gt  using namespace std       int main             string a          cin gt  gt a          switch  string a             case  Option 1               cout lt  lt  It pressed number 1  lt  lt endl              break          case  Option 2               cout lt  lt  It pressed number 2  lt  lt endl              break          case  Option 3               cout lt  lt  It pressed number 3  lt  lt endl              break          default              cout lt  lt  She put no choice  lt  lt endl              break                    return 0             error  invalid cast from type  std  string  aka std  basic string   to type  int

User · Answer

A switch statement can only be used for integral values  not for values of user-defined type  And even if it could  your input operation doesn t work  either   You might want this    include  lt string gt   include  lt iostream gt    std  string input   if   std  getline std  cin  input        error  abort        if  input     Option 1                   else if  input     Option 2                      etc

User · Answer

You can t  Full stop   switch is only for integral types  if you want to branch depending on a string you need to use if else

User · Answer

what about just have the option number    include  lt iostream gt   include  lt string gt  using namespace std   int main         string s      int op       cin  gt  gt  s  gt  gt  op      switch  op        case 1  break      case 2  break      default             return 0

User · Answer

As said before  switch can be used only with integer values  So  you just need to convert your  case  values to integer  You can achieve it by using constexpr from c  11  thus some calls of constexpr functions can be calculated in compile time   something like that     switch  str2int s       case str2int  Value1        break    case str2int  Value2        break      where str2int is like  implementation from here    constexpr unsigned int str2int const char  str  int h   0        return  str h    5381    str2int str  h 1    33    str h       Another example  the next function can be calculated in compile time   constexpr int factorial int n        return n  lt   1   1    n   factorial n-1         int f5 factorial 5       Compiler will run factorial 5      and f5 will be initialized by this value      so programm instead of wasting time for running function      just will put the precalculated constant to f5

User · Answer

You can only use switch-case on types castable to an int   You could  however  define a std  map lt std  string  std  function gt  dispatcher and use it like dispatcher str    to achieve same effect

User · Answer

Switch value must have an Integral type  Also  since you know that differenciating character is in position 7  you could switch on a at 7   But you are not sure the user entered 8 characters  He may as well have done some typing mistake  So you are to surround your switch statement within a Try Catch  Something with this flavour   include lt iostream gt  using namespace std  int main         string a      cin gt  gt a       try           switch  a at 7         case  1           cout lt  lt  It pressed number 1  lt  lt endl          break      case  2           cout lt  lt  It pressed number 2  lt  lt endl          break      case  3           cout lt  lt  It pressed number 3  lt  lt endl          break      default          cout lt  lt  She put no choice  lt  lt endl          break            catch                             return 0      The default clause in switch statement captures cases when users input is at least 8 characters  but not in  1 2 3     Alternatively  you can switch on values in an enum    EDIT  Fetching 7th character with operator     does not perform bounds check  so that behavior would be undefined  we use at   from std  string  which is bounds-checked  as explained here

User · Answer

You can map the strings to enum values  then switch on the enum   enum Options       Option Invalid      Option1      Option2        others        Options resolveOption string input           later     switch  resolveOption input          case Option1                          break            case Option2                          break               handles Option Invalid and any other missing unmapped cases     default                          break            Resolving the enum can be implemented as a series of if checks    Options resolveOption std  string input        if  input     option1    return Option1      if  input     option2    return Option2                return Option Invalid       Or a map lookup    Options resolveOption std  string input        static const std  map lt std  string  Option gt  optionStrings              option1   Option1               option2   Option2                              auto itr   optionStrings find input       if  itr    optionStrings end               return  itr            return Option Invalid

[c++] Evaluate a string with a switch in C++

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