CODEWITHSUNDEEP
c++recursion
Subhadeep Dey
Subhadeep Dey

Reputation: 31

How does recursion work for the following code, since a Boolean OR operation is used in the return statement?

I came across this code, but I couldn't understand how the recursion works for the following code, as there's a Boolean OR operator used within a return statement, which I have never seen before. How is it supposed to work?

bool match(char *first, char * second)
{
    if (*first == '\0' && *second == '\0')
        return true;

    if (*first == '*' && *(first+1) != '\0' && *second == '\0')
        return false;

    if (*first == '?' || *first == *second)
        return match(first+1, second+1);

    if (*first == '*')
        return match(first+1, second) || match(first, second+1); //How does it work?
    return false;
}

Upvotes: 0

Views: 106

Answers (3)

molbdnilo
molbdnilo

Reputation: 66441

It works like all other disjunctions:

First the left-hand side, match(first+1, second) is evaluated.
If it is true, the result of the entire expression is true and nothing else is evaluated.
If it is false, the right-hand side, match(first, second+1) is evaluated and that becomes the result of the entire expression.

Upvotes: 4

alain
alain

Reputation: 12047

An important feature of the boolean operators || and && is short-circuit evaluation. That means in the case of || that if the first call match(first + 1, second) returns true, the second call will not be made, and true will be returned. Else the return value is the returned value of the second call.

Upvotes: 1

lorro
lorro

Reputation: 10880

It works mostly as if a variable were assigned the parameter of return, then that variable returned. The only difference is, the compiler might do return value optimization.

Upvotes: 0

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