With the full code in the question we can now see it’s an integer overflow.
10000 * 180 * 3600 = 6,480,000,000.
This is greater than 2,147,483,648 which is the max value of a 32-bit signed int. The results of the multiplication overflows to -2,109,934,592 and is then converted to double.
To get the right result make one of the numbers a double before you do the multiplication:
10000.0 * 180 * 3600
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solved Multiplication of three numbers in c give a wrong results?