E150 - Spring 1996

Sample Midterm #1
Solutions

Problem #1

Part A

The output is:

2
6
24

Here is the reason why.

i starts out with 1, and n with 2. We enter the loop, check whether i is less than 10, which it is, then multiply i(1) by n(2), which results in i becoming 2. We add 1 to n(2), resulting in n becoming 3. We now write i(2).

We go back to the test, which succeeds, and multiply i(2) by n(3), which results in i becoming 6. We add 1 to n(3), resulting in n becoming 4. We now write i(6).

We go back to the test, which succeeds, and multiply i(6) by n(4), which results in i becoming 24. We add 1 to n(4), resulting in n becoming 5. We now write i(24).

We go back to the test, which fails, terminating the loop.

The problem.

Part B

The output is:

27 9 3
10 6 24

Here is the reason why.

The a in main starts out with 10, and b in mainwith 6. We then call weird passing it 10 and 6.

Within weird, its b is set to 10 and its c is set to 6. We then divide its c by 2, resulting in c being 3. We subtract 1 from b, resulting in it being 9. And we multiply b(9) and c(3) together and store the result (27) in a. We then write this a, b, and c. We return a - c, which is 24, and is stored in the c in the main program. We then write the main's a, b, and c.

The problem.

Problem #2

Part A

The changes are:

• There shouldn't be a semicolon at the end of the #define for MIN_AGE.
• The scanf is missing the ampersand in front of x.
• The comparison in the if should be greater than rather than not equal.
• The if should have a corresponding else separating the printf's.

The problem.

Part B

The changes are:

• The main is missing the prototype for compute_cost.
• compute_cost's first parameter should be a double.
• compute_cost should be declared to return a double, not a void.
• compute_cost needs to divide sales_tax by 100 before using it to compute the final cost.

The problem.

Problem #3

One solution for draw_triangle is:

int draw_triangle(int max_size)
{
  void draw_line(int n);

  int i; 
  int sum;

  sum = 0;
  for (i = max_size; i >= 1; i = i - 1)
  {
    draw_line(i);
    sum = sum + i;
  }
  return sum;
}

void draw_line(int n)
{
  int i;
  
  for (i = 1; i <= n; i = i + 1)
    printf("$");
  printf("\n");
}

The problem.

Problem #4

One solution for this program (that takes into account that there might be no input at all) is:

main()
{
  int value;
  int largest;

  n = scanf("%i", &largest);  
  if (n == 1)   /* got at least one value */
  {
    while (scanf("%i", &value) == 1)
    {
      if (value > largest)
        largest = value;
    }
    printf("The largest input value is %i\n", largest);
  }
  return 0;
}

The problem.

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