Debugging of a function Consider the find_max() function given below: /** Finds the largest value in array elements x[start] through x[last]. pre: first <= last. @param x Array whose largest value is found @param start First subscript in range @param last Last subscript in range @return The largest value of x[start] through x[last]
*/
1. int find_max(int x[], int start, int last) {
2. if (start > last)
3. throw invalid_argument("Empty range");
4. int max_so_far = 0;
5. for (int i = start; i < last; i++) {
6. if (x[i] > max_so_far)
7. max_so_far = i;
8. }
9. return max_so_far;
10.}
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The function will take 3 arguments, an array, starting value and last value and calculates the maximum value and return from where the function has been called. This code does not work properly. In order to understand the working of the code, output statements should be added into the code. The output statements that will be needed in the above function should be inside for loop and after the lines 5, 7 and 9. After including the diagnostic statements, the code can be given as:

/** Finds the largest value in array elements x[start] through x[last]. pre: first <= last. @param x Array whose largest value is found @param start First subscript in range @param last Last subscript in range @return The largest value of x[start] through x[last]
*/
int find_max(int x[], int start, int last)
{
if (start > last) throw invalid_argument("Empty range"); int max_so_far = 0; for (int i = start; i < last; i++)
{
#ifdef TESTING cerr << "x[" << i << "] = " << x[i] << " current max value is " << max_so_far << endl;
#endif
if (x[i] > max_so_far){ max_so_far = i;
#ifdef TESTING cerr << "Value of max_so_far is " << max_so_far << endl;
#endif
} }
#ifdef TESTING cerr << "Returned value is " << max_so_far << endl;
#endif
return max_so_far;
}
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The explanation of all the three output statements can be given as: First output statement can be given as:

#ifdef TESTING cerr << "x[" << i << "] = " << x[i] << " current max = " << max_so_far << endl; #endif This output statement will show the current value of the array that should be compared with the maximum value of the array.
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Second output statement can be given as:
#ifdef TESTING cerr << "max_so_far = " << max_so_far << endl; #endif This output statement will show current value if it is larger than the maximum value.
-------------------------------------------------

Third output statement can be given as:
#ifdef TESTING cerr << "Returning " << max_so_far << endl; #endif This output statement will show the maximum value that will be returned.