Too Many Ifs

Too Many Ifs

Breeze

Member #3,778

August 2003

I want my program to figure out what the user inputed and see what command it was and execute accordingly.

Currently I have like 5 if statements to do this. I am sure there is a better way...

I am not using Allegro...
And I am not very skilled in programming so could you please give a slight in depth response so I know what you are talking about?

Thanks In Advance!;D

Noobie At Programming....
Pathetic Questions Will Be On the Way
Not Using Allegro... Using C++

deps

Member #3,858

September 2003

use switch?

1switch( kbchar )
2{
  case( 'a' ):
  {
      do_this();
      break;
  }
  case( 'b' ):
  {
      do:_that();
      break;
  }
  default:
  {
      do_nada();
      break;
  }
18}

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kazzmir

Member #1,786

December 2001

What do you mean "what the user inputted"? Are you reading in a string from the user? Ill take a stab in the dark here.. Ill assume your program runs like this:

Name an attribute: name
Enter your name: Jon
Name an attribute: age
Enter your age: 20

and then the code you need to do this would be something like

char answer[ 64 ];
while ( something ){
    printf("Name an attribute: ");
    sscanf("%s", answer );
    if ( strcmp( answer, "name" ) == 0 )
        printf("Enter your name");
    else if ( strcmp( anser, "age" ) == 0 )
        printf("Enter your age");
}

Are you doing something like that maybe? Thats pretty much the best way to do it since you cant use a switch statement on strings.

BTW, are you using C or C++? Also, post some code if you want a better answer/response.

DanielH

Member #934

January 2001

If you have an set rule of what was supposed to be inputted you could work around with a switch and if or a loop.

1void check( char *input )
2{
  char *bingo[ 40 ] = { "yo", "sup", "peace out", NULL };
  int i = 0;
5 
  while ( bingo[ i ] )
  {
      if ( strcmp( input, bingo[ i ] ) == 0 )
      {
           switch( i )
           {
               case 0: break;
               case 1: break;
               case 2: break;
           }
16 
           return;
      }

      i++;
  }
22}

1void check( char *input )
2{
  switch ( input[ 0 ] )
  {
      case 'y': 
      {
          if (  strcmp( "yo", input ) } {}
      }
      case 's': 
      {
          if (  strcmp( "sup", input ) } {}
      }
      case 'p': 
      {
          if (  strcmp( "peace out", input ) } {}
      }
  }
18}

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curtis warren

Member #3,898

September 2003

Function pointers? I really can't answer your question any further without you explaining what you mean in depth. Anyways, here's a way you could use function pointers:

1void doHelp(){...}
2void doStuff(){...}
3 
4typedef void (*ptr)();
5 
6std::map<std::string,ptr> table;
7 
8std::string input;
9 
10table.insert(make_pair("help",doHelp));
11table.insert(make_pair("stuff",doStuff));
12 
13cout<<"Please enter a command: ";
14cin>>input;
15ptr p=table.find(input);
16if(p!=table.end())
17{
18   p();
19}
20else
21   cout<<input<<" is not a valid command!";

Btw if there are any mistakes in there let me know-since I haven't used function pointers for a while.

Chris Katko

Member #1,881

January 2002

Hmm. Regardless of using Allegro. The lowest you could get would be a single if statement-per-key scanned.

Except with an array of function-pointers (as mentioned above). But that may be slower then a few ifs.

An if statement is extremely fast relative to seconds. Even on legacy hardware (486s, etc). So if your worried about speed, it's not something that's really taking a chunk of your CPU time. As you mentioned your using 5 ifs. 5 ifs aren't going to do a (noticable) thing to your program.

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curtis warren

Member #3,898

September 2003

Quote:

Hmm. Regardless of using Allegro. The lowest you could get would be a single if statement-per-key scanned.

Except with an array of function-pointers (as mentioned above). But that may be slower then a few ifs.

If your worried about how fast that is you could use the associative container that comes with loki (google it) which is supposedly more efficient than std::map. Not to mention using function pointers like that is much more extensible than if statements.
edit:
Also, if I had a choice to function pointers instead of if statements in a game, I would definately do it, since I would rather worry about extensibility than micro-optimisations. You could, also, use polymorphism, but that is basically just function pointers with a this variable (I wonder if the compiler would optimise the this pointer out if there were no member variables?).

Ceniza

Member #2,027

March 2002

You could get the idea from here.

gillius

Member #119

April 2000

You can't say anything is faster than std::map. There is no code in std::map to profile. You can only say that Loki's implementation of x is faster than Microsoft's implementation of y at providing the same functionality.

Gillius
Gillius's Programming -- https://gillius.org/

Trezker

Member #1,739

December 2001

Hehe, you don't want to read the input code in Devospace, that's chaos if anything.;D

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