Loop Practice

1. Create a program that prints all even numbers from 1 to 50 inclusive. (You must use a loop.)

2. Create a program that prints the first 33 multiples of 3. (3, 6, 9, 12, …, 99)

3. Create a program that prints all numbers between 1 and 100 inclusive, except for numbers evenly divisible by 5.

4. Create a program that prints all multiples of 8 between 8 and 160 inclusive, except for numbers evenly divisible by 3. (8, 16, 32, 40, 56, …)

5. How many times will the following loop run? (Hint: Don’t try to run it)

void the_coolest_loop(void)
{
  int i;

  for (i = 0; i < 10; i--)
  {
    printf("i is %d!\n", i);
  }
}

6. What will the print statements in lines 9 and 17 output? Will it be the same? (You may use a calculator if you want to be exact.) Assume that uninitialized variables in C get assigned garbage values.

void print_sums(void)
{
  int sum;

  for (int j = 0; j != 10; j++)
  {
    sum = sum + j;
  }
  printf("Sum is %d\n", sum);
  printf("Resetting...\n");

  sum = 0;
  for (int j = 0; j != 10; j++)
  {
    sum = sum + j;
  }
  printf("Sum is now %d\n", sum);
}

7. Rewrite the following code to make an equivalent program that uses a for loop, rather than this while loop.

int number = 5;
while (number < 500)
{
  printf("number = %d\n", number);
  number++;
}

8. Rewrite the following code to make an equivalent program that uses a while loop, rather than this for loop.

int items;
int item_cost = 5;
int remaining_dollars = 50;

printf("You have $%d. Let's see how many items you can buy!\n", remaining_dollars);

for (items = 0; remaining_dollars >= item_cost; items++)
{
  remaining_dollars -= item_cost;
}

printf("You bought a total of %d items with your money!\n", items);

9. Is there a difference between the output of these two loops? If so, what is it?

int x;

// Loop 1
x = 0;
while (x < 10)
{
  printf("%d\n", x);
  x++;
}

// Loop 2
x = 0;
do
{
  printf("%d\n", x);
  x++;
} while (x < 10);

10. Fill in the blanks to end the loop if sum > 200.

int sum = 0;

for (int i = 0; i < n; i++)
{
  if (_____)
  {
    _____;
  }

  sum += i;
}

11. What would be printed if the following program runs?

#include <stdio.h>

int main(void)
{
  printf("We are starting the loop!\n");

  for (int i = 0; i < 5; i++)
  {
    if (i == 3)
    {
      return 0;
    }

    printf("i = %d\n", i);
  }

  printf("We are ending the loop!\n");

  return 0;
}

12. What would be the return value of loopy_loop() if executed?

int loopy_loop(void)
{
  int x = 0;

  while (x < 10)
  {
    printf("x = %d\n", x);

    if (x == 5)
    {
      return 2;
    }

    x += 2;
  }

  return 5;
}

13. Write a program that finds the sum of all integers that a user types in, then when the user types 0, the final sum will be displayed and the program ends. The following is an example of running the program:

5
10
4
-9
0
The sum is: 10

14. Write a program that prints an n by n “addition table.” An addition table is like a multiplication table, except the row and column numbers are added instead of being multiplied. For example, the following is a 5x5 addition table.

0   1   2   3   4
1   2   3   4   5
2   3   4   5   6
3   4   5   6   7
4   5   6   7   8

15. Challenge: Write a program that prints a diamond shape with a height of n. Assume that n is greater than 2 and is odd. As an example, the following is a diamond with a height of 5.

  #
 # #
#   #
 # #
  #