4.2 Problem Solving: Hand-Tracing Hand-tracing is a simulation of code execution in which you step through instructions and track the values of the variables. In Programming Tip 3.6, you learned about the method of hand-tracing. When you hand-trace code or pseudocode, you write the names of the variables on a sheet of paper, mentally execute each step of the code and update the variables. It is best to have the code written or printed on a sheet of paper. Use a marker, such as a paper clip, to mark the current line. Whenever a variable changes, cross out the old value and write the new value below. When a program produces output, also write down the output in another column. Consider this example. What value is displayed? int n 1729; int sum = 0; while (n > ) int digit n % 10; sumsum digit; n n10; cout