Programming

Question

rec(int x)
{
    static int f;
    if(x==1)
    return 1;
    else
    f+=x*rec(x-1);
    return(f);
}

the value returned by rec(5) is_____________

Comments

It should be 240

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can u explain or give reference

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Wouldn't this result in undefined behaviour?

https://gateoverflow.in/60/gate2013-42

Answer 1

initially  f should be initialized to 0

so f=0

function f=f+x*rec(x-1)

rec(1)=1

f(2)=0+2*rec(1)=2

f(3)=2+3*rec(2)=8

f(4)=8+4*rec(3)=40

f(5)=40+5*rec(4)=240

s0 f returns 240

Comments

same value taking 2 times rec and f

Answer 2

rec(5)-> f=f+(5*rec(4))=240

rec(4)->f=f+(4*rec(3))=40

rec(3)->f=f+(3*rec(2))=8

rec(2)->f=f+(2*rec(1))=2

rec(1)=1

so answer of rec(5) is 240

Comments

explain a bit more

how getting f value

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always evaluate function from base i.e from f(1)

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thanks:)

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For static variable and global variable default value will be zero and for global variables default value will be garbage value.For static varibale lfe time is through out the program and memory is allocated only once.

so initially f=0

rec(1)=1

rec(2)->f=f+(2*rec(1))=0+2*1=2

rec(3)->f=f+(3*rec(2))=2+3*2=8

rec(4)->f=f+(4*rec(3))=8+4*8=40

rec(5)-> f=f+(5*rec(4))=40+5*40=240