Having trouble with case loop

Question

please. I want a display for options from 'A' to 'H', however the "default invalid option" kept appearing. How do i prevent the "default invalid option from apprearing. Thanks so much if you could give me a hand.

void disp3Ave (void)
{
    int day, total;
    char j;
    extern float PSI23ave[];
    extern float PSI24ave[];
    extern float PSI25ave[];
    float average;
    total=0;
    printf("Day 23 or 24?\n");
    scanf("%\d", &day);

    if(day == 23)
    {
        printf("A: 0300.\n");
        printf("B: 0600.\n");
        printf("C: 0900.\n");
        printf("D: 1200.\n");
        printf("E: 1500.\n");
        printf("F: 1800.\n");
        printf("G: 2100.\n");
        printf("H: 0000.\n");
        scanf("%c", &j);

        switch (j)
        {
            case 'a':
            case 'A': total= PSI23ave[3] + PSI23ave[4] + PSI23ave[5];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;
            case 'b':
            case 'B': for (j=0;j<24;j++) total= PSI23ave[6] + PSI23ave[7] + PSI23ave[8];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;
            case 'c':
            case 'C': for (j=0;j<24;j++) total= PSI23ave[9] + PSI23ave[10] + PSI23ave[11];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;
            case 'd':
            case 'D': for (j=0;j<24;j++) total= PSI23ave[12] + PSI23ave[13] + PSI23ave[14];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;
            case 'e':
            case 'E': for (j=0;j<24;j++) total= PSI23ave[15] + PSI23ave[16] + PSI23ave[17];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;
            case 'f':
            case 'F': for (j=0;j<24;j++) total= PSI23ave[18] + PSI23ave[19] + PSI23ave[20];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;
            case 'g':
            case 'G': for (j=0;j<24;j++) total= PSI23ave[21] + PSI23ave[22] + PSI23ave[23];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;
            case 'h':
            case 'H': for (j=0;j<24;j++) total= PSI24ave[0] + PSI24ave[1] + PSI24ave[2];
                  average = total/3;
                  printf("3-hr average = %.1f\n", average);
                  break;

            default: printf("Invalid option.\n");
                 break;

        }
    }

Thanks in advance! cheers!

Answer 1

As user1990169 concluded, the issue is that the buffer reads the integer from stdin, but the newline character remains in the input buffer. This can be addressed in a number of ways, but the simplest is to add a call to getchar() which will read one character from the input stream.

scanf("%d", &day); // remove the \ before d
getchar();

---

here's a small program to demonstrate:

int main(void) {
  int day = -1;
  char c = 'x';
  scanf("%d", &day);
  getchar(); // this line
  scanf("%c", &c);
  printf("read: %d %c\n", day, c);
}

if you remove the call to getchar() you'll see that there is no wait before reading the character, it will just immediately read a newline into the c variable.

There are more advanced options to deal with input separated by an unknown number of spaces using isspace and ungetc, but for your simple program, this should suffice.

Additionally, instead of having a case for the uppercase and lowercase, you can convert the character and only have one case label for each:

j = toupper(j); // #include <ctype.h>

Answer 2

It appears that when you enter the value for the int variable day, the character '\n' remains in the input buffer.
This gets stored in your variable j and hence you get Invalid option.

Edit: You can try scanf("\n%c", &j);