Mine

#include <stdio.h>

/* Replacement resistance. */
int ohm_calc(float ampere, float volt, float ohm)
{
	float result = 0;

	if((ampere == 0) && (volt == 0) && (ohm == 0))
	{
		printf("You have to give at least two values.\n");
	}

	if(ampere == 0)
	{
		result = volt / ohm;
		printf("Volt: %f\nOhm: %f\nAmpere: %f\n", volt, ohm, result);
	}

	if(volt == 0)
	{
		result = ohm * ampere;
		printf("Volt: %f\nOhm: %f\nAmpere: %f\n", result, ohm, ampere);
	}

	if(ohm == 0)
	{
		result = volt / ampere;
		printf("Volt: %f\nOhm: %f\nAmpere: %f\n", volt, result, ampere);
	}

	return 0;
}
/* Main function */
int main()
{
	int which;
	float volt, ampere, ohm;
	int i;
	int size;
	printf("What do you wanna calculate?\n0 = Ohm, Ampere or Voltage.\n1 = Replacement resistance.\n\n");
	printf("Choose:_\b");
	scanf("%d", &which);
	switch(which)
	{
		case 0:
			printf("Welcome. Give me the values of Ohm, Ampere and Voltage.\n");
			printf("The one you set as 0 is the one that is going to be calculated.\n");
			printf("Volt:_____\b\b\b\b\b");
			scanf("%f", &volt);
			printf("Ampere:_____\b\b\b\b\b");
			scanf("%f", &ampere);
			printf("Ohm:_____\b\b\b\b\b");
			scanf("%f", &ohm);
			ohm_calc(ampere, volt, ohm);
			break;

			case 1:
				printf("Give me how many numbers you are going to use.\n");
				printf("Size:__\b\b");
				scanf("%d", &size);
				float rr[size];
				for(i = 1; i <= size; i++)
				{
					printf("Give me number %d:", i);
					scanf("%f", &rr[i]);
					printf("You gave me %f\n", rr[i]);
				}
				float result = 0;
				for(i = 1; i <= size; i++)
				{
					result = result + (1 / rr[i]);
				}
				result = 1 / result;
				printf("Result: %f\n", result);
			break;
	}
	return 0;
}