Validation

Code:

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do         
 {
                // prompt and read salesman id
                printf("Salesman ID (NO.): ");
                scanf("%d",&stop);
                if (stop == NULL)
                {
                    valid = 0;
                    printf("Invalid input. Please input again.\n\n");
                }
                else
                    valid = 1;
            } while (valid == 0);

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How can I fix it to avoid the continuous looping?

scanf returns the number of items that it successfully converted. Check that it returns 1. If it doesn't return 1 you'll need to clear the input buffer before you try to call scanf again (and NOT with fflush(stdin)).

Edit: unless, of course, it returns EOF, then you will probably want to exit or something because that's a read error or end-of-file condition.

FAQ > Why fflush(stdin) is wrong - Cprogramming.com
Does it matter if behaviour is undefined?

FAQ > Flush the input buffer - Cprogramming.com
I can't understand how it works. :confused:

Quote:

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Does it matter if behaviour is undefined?

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Um, yes. A program is supposed to behave in a predictable manner. If it doesn't, then it is useless, if not downright dangerous.

http://faq.cprogramming.com/cgi-bin/...&id=1043284392
So, is it means keeping moving the input buffer to ch and reset it just like no input before? Is \n also loved to ch? What is the purpose of EOF? The program still works fine without EOF.

Anybody can help me?:biggrin:

Quote:

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Originally Posted by ulti-killer

Anybody can help me?:biggrin:

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From MSDN site:
"To indicate a read error or end-of-file condition, getc and getchar return EOF"

And the reason that you keep getting things off the stdin until '\n' is found is because it is most likely the last thing that was entered.

Is \n also moves to ch too?

Keyboard input is generally line buffered. This means that when you type something, it's stored in a buffer and your program does not see it, until it encounters a newline character, which flushes the input buffer (sends it to your program, in this case).

So, if you type "abc" followed by 'enter', there are four characters in the input buffer.

Code:

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abc\n

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Now, if you use "getchar()", it takes a single character from the input buffer.

Code:

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// input buffer contains "abc\n"

int cInput;

cInput = getchar();  // takes the 'a' from the input buffer
putchar(cInput);    // prints 'a' to the output (screen)

cInput = getchar();  // takes the 'b' from the input buffer
putchar(cInput);    // prints 'b' to the output (screen)

cInput = getchar();  // takes the 'c' from the input buffer
putchar(cInput);    // prints 'c' to the output (screen)

cInput = getchar();  // takes the '\n' from the input buffer
putchar(cInput);    // prints '\n' to the output (screen)

// the input buffer is now empty

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This is why, in that link, we use '\n' to determine when a single line has been entered. The program receives the user input, and each character is plucked, one by one, from the input buffer until the newline (where we know it ends, for that line) is read. (Click_here already covered the other option, EOF.)