How does this become zero just by adding long double

[civic burrow]

#include <stdio.h> int main() { double sum = 1; double term = 1; int k = 0; for(; k < 10000; ++k) { term = term*2*(k+1)*(k+1)/((2*k+2)*(2*k+3)); sum = (long double) sum+term; } sum *= 2; printf("%Lf", (long double) sum); return 0; }
So if i remvoe the (long doubles) the value will be as expected, but long double turns it to 0.000 for some reason?

[iron rapids]

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[hollow basalt]

;compile

#include <stdio.h>
int main() {
    double sum = 1;
    double term = 1;
    int k = 0;
    for (; k < 10000; ++k) {
        term = term * 2 * (k + 1) * (k + 1) / ((2 * k + 2) * (2 * k + 3));
        sum = (long double)sum + term;
    }
    sum *= 2;
    printf("%Lf", (long double)sum);
    return 0;
}

[mint minnow]

Program Output

3.141593

hisarya | 44ms | c | x86-64 gcc 14.2 | godbolt.org

[hollow basalt]

unable to reproduce

[plucky viper]

because long double is broken on windows