I'm still new to C and I dont have a clue why my float result is random (maybe type promotion rules?)

Question

I believe that it has something to do with type promotion rules, but I'm not sure and considering the fact that I'm still new to programming, I cant imagine why this:

#include <stdio.h>

int main() {

    float result;
    result = function(2.4, 4.9);

    printf("Test: %.2f\n", result);
    system("PAUSE");
    return 0;
}

float function(float value1, float value2) {
    float calculation = value1 * value2;
    return calculation;
}

would print out

Test: -858993472.00

I'm typing in float values and I want my calculation to return an other float value as my result, what am I doing wrong?

Answer 1

Declare the function before you invoke it. Here you need to put the definition above main() or just put a declaration before main.

#include <stdio.h>

float function(float value1, float value2) {
    float calculation = value1 * value2;
    return calculation;
}
int main() {

    float result;
    result = function(2.4, 4.9);

    printf("Test: %.2f\n", result);

    return 0;
}

Or

#include <stdio.h>

float function(float value1, float value2);
int main() {

    float result;
    result = function(2.4, 4.9);

    printf("Test: %.2f\n", result);

    return 0;
}
float function(float value1, float value2) {
    float calculation = value1 * value2;
    return calculation;
}

Also if you have turned on the warning then you will possibly see a message like this

..: 'function' was not declared in this scope