How truncate a value in c++ builder 6?

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C++

Hello again,
I was testing to truncate a value with how many decimals case i want.
Nice, i found a function that make this, but, use double, and i need to use float,
double is crashing everything with StackOverFlow errors that i can't fix.
And with float that works..
This is the code of the function.

double trunc(double value, int decimal_places){
    double integer = 0,fractional = 0,output = 0;
    int j = 0,places = 1;
    fractional = modf(value, &output);
    for( int i = 0; i < decimal_places + 1; i++ ){
        fractional = modf(fractional, &integer);
        for( j = 0; j < i; j++ ){
            places *= 10;
        }
        output += integer / places;
        places = 1;
        fractional *= 10;
    }
    return output;
}

Thanks