program to accept three numbers from the user and print them in ascending and descending order using if else if ladder

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Write a program to swap the values of two variables without using third variable
step 1-
a=a+b,the two values entered by user will be added and get stored in a
for ex: if user enter 30 and 10.
a=a+b
a=30+10
a=40.
step 2:
now the value of a is 40 and b is 10
b=a-b
b=40-10
b=30
step 3:
now the value of a is 40 and b is 30
a=a-b
a=40-30
a=10


now value of a=10,b=30
hence numbers got swapped

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Write a program to calculate the area and perimeter of the circle