Floating point math in c getting random numbers [closed] - c

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I'm doing a exercise from C primer plus that involves working with floats, I can't get the result to also be a float. I got it to read in the input fine (as far as I can tell) but the problem must be in the formula line. Can anyone tell me what I'm doing wrong?
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
float inp1, inp2;
float result;
result = (inp1 - inp2) / (inp1 * inp2); /* formula */
printf("enter two values\n");
scanf("%f %f", &inp1, &inp2);
printf("(%.3f - %.3f) / (%.3f * %.3f)\n", inp1, inp2, inp1, inp2);
printf("%f\n", result);
}
The output is giving some random number (I don't know what it's called), for example with an input of 1.255 and 1.023 I get an output of 2656044210243861500000000000000000000.000000 or something similar. The second to last printf displays the input correctly.
What am I doing wrong?
I've tried this, but I don't really get how cast operators work.
result = ((float)inp1 - (float)inp2) / ((float)inp1 * (float)inp2); //formula
and
result = (float)(inp1 - inp2) / (inp1 * inp2);

Answer 1

result = (inp1 - inp2) / (inp1 * inp2); /* formula */
printf("enter two values\n");
scanf("%f %f", &inp1, &inp2);
Well, what about putting scanf call before result = ...; assignment statement?

Answer 2

result = (inp1 - inp2) / (inp1 * inp2); /* formula */
printf("enter two values\n");
scanf("%f %f", &inp1, &inp2);
That's not how things work in a language like C; you don't define a formula for result that's automatically computed when you read your inputs. Rather, you first read your inputs, and then you compute the value and assign it to result:
printf("enter two values\n");
scanf("%f %f", &inp1, &inp2);
result = (inp1 - inp2) / (inp1 * inp2); /* computation and assignment */
C is an imperative language, meaning you have to explicitly list out the instructions for it to follow, including those for any mathematical computations.

Answer 3

The analogy of math formulas in programming languages is functions (without side effects). That way, you can define formulas before the code itself. For instance:
#include <stdio.h>
#include <stdlib.h>
float formula(float inp1, float inp2)
{
return (inp1 - inp2) / (inp1 * inp2);
}
int main(void)
{
float inp1, inp2;
printf("enter two values\n");
scanf("%f %f", &inp1, &inp2);
printf("(%.3f - %.3f) / (%.3f * %.3f)\n", inp1, inp2, inp1, inp2);
printf("%f\n", formula(inp1, inp2));
return 0;
}