Sometimes you want one function to make changes in the variables of a different function. For example, a common task in sorting problems is interchanging the values of two variables. Suppose you have two variables called x and y and you want to swap their values. The simple sequence
x = y; y = x;
does not work because by the time the second line is reached, the original value of x has already been replaced by the original y value. An additional line is needed to temporarily store the original value of x.
temp = x; x = y; y = temp;
Now that the method works, you can put it into a function and construct a driver to test it. To make clear which variables belong to main() and which belong to the interchange() ...