c - Why does the program return with an exit code other than I specified?

Question

This is a simple program :

int main() {
    return 0;
}

The exit code is 0.

If I write:

int main() {
    return 700;
}

The exit code is 188.

Why is 188 instead of 700 the exit code here?

Answer 1

While the main function in C returns an int, operating systems don't necessarily use int as the error code.

700 in binary is 1010111100.
Truncating this value to eight bits yields 10111100.
This equals 188 in decimal.

That means your OS uses eight bits for error codes.¹

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¹ Or possibly nine bits because the 8^th bit (we start counting from 0, mind you) is 0 here. This is highly improbably due to 9 not being a power of 2, though, as is convention for data widths.