How to declare for assembly functions, multiplication, divison, and substraction can you please declared and include the codes in the following program codes for the calculator to work and please explain how the codes works? #include

extern int add$($int a$,$ int b$)$;

int main$()\{$

printf$("$Choose operation $(+,-,*,/)$: $")$;

char operation;

scanf$("\%$c$",$ &operation$)$;

printf$("$Enter first number: $")$;

int num$1$;

scanf$("\%$d$",$ &num$1)$;

printf$("$Enter second number: $")$;

int num$2$;

scanf$("\%$d$",$ &num$2)$;

int result;

switch $($operation$)\{$

case $\text{'}+\text{'}$:

result $=$ add$($num$1,$ num$2)$;

break;

default:

printf$("$Invalid operation

$")$;

return $1$;

$\}$

printf$("$Result: $\%$d

$",$ result$)$;

return $0$;

$\}$