Variable in for loop not behaving as expected. [C17]

December 24, 2023

I’m trying to create a piece of code that would divide a set amount of money into their biggest bills constituents. Say, Input = 1200, then the code would print "[2]500 bills, [1]200 bills".

However using said Input the code would print "[2]500 bills, [2]100 bills". If I add a printf("%d",i); to see how the i values changes through the loop is does on a seemingly random manner; it also depends on the input given? Why?!
I can’t get my head around of why this is happening.

Code

#include <stdio.h>
#include <math.h>

int main()
{
    float Input;
    scanf("%f",&Input);
    int SizeBilletes[7] = {500,200,100,50,20,10,5};
    for(int i=0;i<7;i++){
        if(Input/SizeBilletes[i]>1){
            int a = floor(Input/SizeBilletes[i]);
            Input -= a*SizeBilletes[i];
            printf("[%d] en Billetes de %d\n",a,SizeBilletes[i]);
        }
    }
}

Important Notes:

The Input has to be a float as the user might add a value that isn’t an integer (like cents or penys)
If instead of a loop I use a ton of if statements to evaluate each size individually it works like a charm
Using "Input %= SizeBill[i]" give me an error (was a solution given on a discord community)
I’m very new to programming so apologies in advance if this is quite a simple problem.