C :: How Arguments Handled If Passing Parameters Are Different Types Compared To Declaration

Suppose if i write a test program like

Code:
void function1(unsigned int var1);
int main(void) {
function1(-3);
}
void function1(unsigned int var1) {
printf("%d", var1);
}

The output is -3. how it happens the argument is unsigned but iam passing signed but still prints the signed value. My bigger question is how the arguments are handled if the passing parameters are different types compared to declaration.