CODEWITHSUNDEEP
c
user968000
user968000

Reputation: 1843

Why this function is running in an infinite loop?

I am trying to learn about recursion. I dont understand why the following piece of code runs in an infinite loop? 

void myFunc(int n)
{
     if(n==0)
         return;
     else
     {
         printf("%d\n",n);
         myFunc(n--); //if I put n=n-1 before this line then it is running fine and will exit from the function .
         printf("%d\n",n); 
     }

}

int main()
{

    myFunc(4);
}

Upvotes: 1

Views: 152

Answers (6)

krish7919
krish7919

Reputation: 942

n-- and --n are different. You should look up C operators and sequence points for the explanation. Basically, n-- means 'use n and decrement it at the next sequence point', whereas --n means 'decrement n first and then use it'..

Upvotes: 1

Thomas Hobohm
Thomas Hobohm

Reputation: 645

N-- is a postfix operator. This means that it will increment the variable you are using it on after the value is used. As an example, in the expression x * y--, the compiler will return x * y, and then decrement y.

Upvotes: 0

Michael Greene
Michael Greene

Reputation: 10423

-- is a post-decrement operator as you are using it and only takes effect after myFunc is called with the value of n, so you will be calling myFunc with the same value over and over again.

Using it as a pre-decrement operator would fix your particular use case: myFunc(--n) would have a similar effect to putting n=n-1 on the line before.

Upvotes: 7

Simon
Simon

Reputation: 10841

n-- decrements n after n is passed to myFunc(), so myFunc is receiving the same n value every time it is called.

Upvotes: 3

dan
dan

Reputation: 1002

n-- calls the postfix operation, which means the value of n gets passed into myFunc. After that, n's value is decremented by one. Call myFunc(--n).

Upvotes: 4

MAV
MAV

Reputation: 7457

Because the decrement is performed after the call. Not before.

If you do myFunc(--n); instead, it will work

Upvotes: 3

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