In my recent interview, a well known company in ahmedabad having branches in all over India, I was asked to write a programm. I have to swap the values of three variables without using fourth varable. I found it really triky. I will first explain this with two variables and than show for three variables in two diffrent ways.

Lets, consider the case a = 10 and b=20. I have to write the programm so that result will be a= 20 and b= 10. Below is the steps,

a = 10;

b=20;

a = a+b; ( a= 30)

b = a - b; (b = 30 - 20 =10)

a = a-b; (a = 30-10 = 20)Fig - 1 Steps to swap the values of two variables.

Now take three variables, a= 10, b=20 and c =30. The output should be a=30, b=10 and c= 20. First way to achive this is you can use steps mentioned in Fig -1 three times. First swap a and b than a and c. Below is the steps,

a = 10;

b=20;

c=30;

a = a+b; ( a= 30)

b = a - b; (b = 30 - 20 =10)

a = a-b; (a = 30-10 = 20)// Here a= 20 and b= 10;

a = a+c; ( a= 20 + 30 = 50)

c = a - c; (c = 50 - 30 =20)

a = a-c; (a = 50-20 = 30)// Here a= 30 and c= 20;

Fig - 2 Steps to swap the values of three variables.

Second way of swapping the values of three variable is,

a = 10;

b=20;

c=30;

a = a+b+c; ( a= 60)

b = a - (b+c); (b = 60 - (20+30) =10)

c = a- (b+c); (c = 60 - (10 + 30) = 20)

a = a- (b+c); (a = 60 - (10 + 20) = 30)

Fig - 3 Steps to swap the values of three variables.

Happy Programing.

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