C Programming

Question

What will be output of below program

#include<stdio.h>
int tech(int,int);
int main(void){
    int a=tech(15,4);
    printf("%d",a);
    return 0;
}
int tech(int p,int q){
    if(p%q==0)
    return q;
    else
    tech(q,p%q);
}

Comments

Returning GCD.

Test cases T(20,15), T(6,3) T(3,6)

Answer 1

The given program finds the gcd of the two numbers using long division method recursively . We can show it here : 

tech (15 , 4)   ==>  tech (4 , 15 % 4)  = tech (4 , 3)

                    ==>   tech(3 , 4 % 3)    =  tech(3,1)

                    ==>   tech(3 , 1)           =  1     as  3 % 1 == 0

Hence return value of the function is 1.

Also if we see gcd(15,4) , it is also 1.

Hence the output of the given program is 1 .

Comments

@Habib

After each call there is a printf statement

But here printing done 1 time.

Because, it is storing the value of "a" at last only , right?

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I thought 3 times 1 will print

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int main(void){
    int a=tech(15,4); one time call happen here, once it done i.e. value return from call then printf work
    printf("%d",a);
    return 0;

}

int tech(int p,int q){    1st call arrive here.
    if(p%q==0)
    return q;
    else
    tech(q,p%q);  from 2nd time call will happen from here only , so call tech(15,4) will terminate when it return value which is q   . this function ecall itself and terminate by returing only one value which is q=1 here.
}

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Printing will be done once onlu @srestha as printf() is used in main() only and called only once.

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and printing is done after storing the result in a

and not each time when function called

that is why 1 time printing will be executed

right?

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Yup exactly @srestha.

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ok tnks @Prasant @Habib

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@srestha @habibkhan Shouldn't there be a return statement in else of tech function?

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Yes there should be return statement in else part as well

Answer 2

here is my answer.

Comments

call by value in return time value will not change in main()

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@Prashant ur comment in 1st ans is not readable yr

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now check