function pointer calculator

[bertazoid]

Hi, I'm trying to learn about function pointers and how to use them.

I have the following partially written program in c for a simple calculator, and without using a switch statement, how can I complete it using function pointers?

//declare functions

float plus(float a, float b) { return a+b; }
float minus(float a, float b) { return a-b; }
float times(float a, float b) { return a*b; }
float divide(float a, float b) { return a/b; }

int main() {

//declare function pointers

  float(*fptr_p)(float, float);
  float(*fptr_m)(float, float);
  float(*fptr_t)(float, float);
  float(*fptr_d)(float, float);

//point ptr's to functions

  fptr_p=+
  fptr_m=−
  fptr_t=×
  fptr_d=÷

return 0;
}

usually I would get the input from the command line here, and use a switch statement. This is probably the easiest way of doing things, and function pointers need not be used, but I'm sure there is a way of using them for this, and I can't think how. I'm just about familiar withn how to pass a function pointer as an argument of a function and how to return a function pointer from a function, but I can't see how this gets rid of the need for a switch statement.

[matsp]

You still need some way to translate from '+' to the function for addition. You could do this by having a translation from + to an enumerated value, eg. OP_PLUS, and then use OP_PLUS as an index into an array of function pointers.

Or you could make an array of 128 elements, and let only those that correspond to '+', '-', '/', '*' be set to non-NULL value, and then use the operator character as an index into the array.

--
Mats

[bertazoid]

Thanks, I'll give it a try.

[matsp]

By the way, would it not make more sense to declare ONE function pointer typedef for all 2-operand operators - after all, the operators all take the same two operands in the same order and way.

--
Mats