Question

So I’ve been working on the Harvard CS50 course on iTunes U and have run into a bit of a problem. The code runs and then stops. I explain the issue where the code is giving me trouble.

// Program calculates the amount of change you can give with the least amount of coins.

 #include <stdio.h>
 #include <cs50.h>
 #include <math.h>

int
main(void)
{

    float change = 0, inputflag = 1;
    int changeint = 0;
    int quarter = 25, dime = 10, nickel = 5, penny = 1; // Coins and values
    int qc = 0, dc = 0, nc = 0, pc = 0; // Coin value change (Qc = Quarter Change)

// Prompts user for input and validates. 

    while (inputflag == 1)
     {
        printf("How much change? ");
        change = GetFloat();

        if (change == 0)
        {
            printf("You have no change!\n");
            inputflag = 0;
        }
        else if (change > 0)
        {
            printf("%.2f\n", change);
            inputflag = 0;
        }
        else
        {
            printf("Please enter a non-negative number! \n");
        }
     } 

The program stops here. I run the code, input an acceptable value and then the program stops running. It doesn’t move onto the part below.

I have spent the last hour going over this and still can’t figure out what is keeping the program from running. The inputflag value gets set to 0 thus breaking the first while loop and then should move on below if (change != 0) which it doesn’t…So any advice would be greatly appreciated.

    if (change != 0) // If the change is zero, this section is skipped
        {
            changeint = round(100 * change);
            printf("%d", changeint);
        }

      // The following four sections subtract coin amount, compare it, and add 1 to count.  
          while (changeint >= quarter);    
          {   
               changeint = changeint - quarter;
               qc = qc + 1;
          }

          while (changeint >= dime);
          {
               changeint = changeint - dime;
               dc = dc + 1;
          }

          while (changeint >= nickel);
          {
               changeint = changeint - nickel;
               nc = nc + 1;
          }

          while (changeint >= penny);
          {
               changeint = changeint - penny;
               pc = pc + 1;
          }

//Prints output

          printf("You owe a total of %d coins!", qc + dc + nc + pc);

}

Answer 1

The semi-colons at the first line of each while statement are to blame. You should remove them to avoid an inevitable infinite loop:

      while (changeint >= quarter) 
      {   
           changeint = changeint - quarter;
           qc = qc + 1;
      }

      while (changeint >= dime)
      {
           changeint = changeint - dime;
           dc = dc + 1;
      }

      while (changeint >= nickel)
      {
           changeint = changeint - nickel;
           nc = nc + 1;
      }

      while (changeint >= penny)
      {
           changeint = changeint - penny;
           pc = pc + 1;
      }

Yes, even the simplest of problems might go undetected, and for/while statements with semi-colons are one of them (which could be intended).