Write a program to calculate area of a circle using functions.

area = (atan(1) * 4) * (pow(radius, 2));

GET the PI value

atan(1) = PI/4 * 4 = PI

Pow

Use pow function to exponentiation.

Write a program to swap two values using functions.

Write a program to convert time to minutes using functions. (input 3 variables namely hours, minutes and seconds. Convert everything into minutes.)

Cin.fail Cin.clear Cin.ignore

We can use this cin function to judge the user input's correctless. If cin.fail is 1, maybe our input type is wrong with the store variable type.

cin.clear(); // Clear the error state

cin.ignore(std::numeric_limitsstd::streamsize::max(), '\n');//clear all input in the string buffer

Write a program to sum the series up to n (Input n)