Thread: Need ideas on how to improve my code

By 'formula' do you mean 'do the calculation' ? You need to clarify some things, maybe post some actual code, at present your members of the struct are all char arrays, they can only hold that data, ie strings, so do you wish your program to simply retreive the type of formula, stored by its terms as characters? or its name? according to the input values the user enters?
If you write in C++ you can use classes which would contain a working conversion function - also templates might be of use, but it is more advanced, try reading this

So pick a baseline unit, say metres, then have
miles to metres
followed by
metres to kilometres

If you're converting "to" the baseline, use fn()
If you're converting "from" the baseline, use 1/fn()

Originally Posted by NumLock

It would now be easy to just search through the array until units[i].from and units[i].to matches user inputs, and then read the units[i].formula to get the formula.

Okay, but IMO that is just moving some code around that might as well be dealt with in nested (rather than parallel) if's:

Code:

//pseudo
if (convert_from == kilometers) {
      if (convert_to == miles)  return convert_from / 1.6;
      if (convert_to == feet) return convert_from / 1.6 * 5280;
      return invalid;
}

You only have to deal with valid cases; eg, converting km to Fahrenheit is the same as converting pounds to minutes.

You are basically looking at two problems here, (1)how you want to implement your lookup table, and then (2)how to perform the calculations:

1. The easiest version of a lookup table would simply to make an array of structures, whereas the structures contained two members: the conversion "name" and then the formula.

2. The second part of your problem is processing the formula, which is essentially just a "create a calculator" problem. There are many ways to do this, you could look at how RPN is calculated to give you an idea.

Here is an example that uses a very simple calculator just to give you the idea:

Code:

#include <stdio.h>
#include <string.h>
#include <ctype.h>

struct table{
	char conversion[50];//user inputted conversion
	char formula[50];//holds 50 char to implement formula
};

int simpleCalculator(char [], int);

int main(void){

	char myInput[10]={0}, inputbuffer[100]={0};
	int num1=0, answer=0;
	//implement our lookup table, this would be loading from a file
	struct table LookupTable[]= {{"c->k","+ 273"},
				     {"km->m","* 1000"}};

	//obtaining user input, this would be cmd line args entered
	//like: m->km 3000
	printf("Enter cmdLine args:");
	fgets(inputbuffer,sizeof(inputbuffer),stdin);
	sscanf(inputbuffer,"%s %d", myInput, &num1);
	//------------------------------------------------

	//now we find the value in our lookup table and call our calculator
	for(int i = 0; i < (sizeof(LookupTable)/sizeof(table));i++){
		if(strcmp(LookupTable[i].conversion,myInput)==0){
			answer=simpleCalculator(LookupTable[i].formula, num1);
			break;
		}
	}

	printf("Answer = %d", answer);
	getchar();
	return (0);
}
int simpleCalculator(char formula[],int input){

	int factor=0, answer=0;
	char operand;

	sscanf(formula,"%c %d", &operand, &factor);

	switch(operand){
		case '*':
			answer = input * factor;
			break;
		case '+':
			answer = input + factor;
			break;
	}

	return answer;
}