Why do we designate one of the candidate keys of a relation to be the primary key?

In this lab, you add a loop and the statements that make up the loop body to a c++ program that is provided. when completed, the program should calculate two totals: the number of left-handed people and the number of right-handed people in your class. your loop should execute until the user enters the character x instead of l for left-handed or r for right-handed. the inputs for this program are as follows: r, r, r, l, l, l, r, l, r, r, l, x variables have been declared for you, and the input and output statements have been written.

In excel - calculate the actual increase/decrease from first quarter to the second quarter then subtract subtract first quarter value from second quarter total then divide result by first quarter value

Write a program that displays the following menu: geometry calculator 1. calculate the area of a circle 2. calculate the area of a rectangle 3. calculate the area of a triangle 4. quit enter your choice (1-4): if the user enters 1, the program should ask for the radius of the circle and then display its area. use the following formula: area = ď€(the square of r) use 3.14159 for ď€ and the radius of the circle for r. if the user enters 2, the program should ask for the length and width of the rectangle and then display the rectangle’s area. use the following formula: area = length * width if the user enters 3, the program should ask for the length of the triangle’s base and its height, and then display its area. use the following formula: area = base * height * .5 if the user enters 4, the program should end. input validation: display an error message if the user enters a number outside the range of 1 through 4 when selecting an item from the menu. do not accept negative values for the circle’s radius, the rectangle’s length or width, or the triangle’s base or height. note: if the user enters an improper menu choice (1-4), the program prints "the valid choices are 1 through 4. run the program again and select one of those." if the user enters a negative radius, the program prints "the radius can not be less than zero." if the user enters a negative value for height or base, the program prints "only enter positive values for base and height."