Thread: Simple Scanf and printf

Hey guys... I am currently taking a C progarmming class, and I've been unable to contact my instructor and I've reached a little snag in code

It seems as though this program randomly crashes. I can't input any hyphens or anything more than about 50 characters without it crasahing. Its terribly confusing, and I have no idea why it isn't working.

Edit: Also the program ends prematurely if I enter long text for the two previous strings.

Here it is:

Code:

//This program accepts input a greeting, name and email and then displays
// that information to the user.


   #include <stdio.h>

   int main(void)
   {

       char inEmail[500];
       char inName[500];
       char inMessage[150];
       char exitKey;

       printf("Enter a greeting message: ");
       gets(inMessage);


       printf("Enter a name please: ");
       scanf("%s",&inName);

       printf("Enter your email address: ");

       scanf("%s",&inEmail);


       printf("%s\n",inMessage);
       printf("Your name is %s\n",inName);
       printf("Your email address is %s\n",inEmail);

       printf("Press return to exit program:");
       scanf("%c",&exitKey);

       getchar();


       return 0;

   }

The only thing that's actually wrong with your code is how you put an ampersand before an array in your scanf() calls, here:

Code:

scanf("%s",&inName);

and here:

Code:

scanf("%s",inEmail);

Then of course, there's the usual argument that neither gets nor scanf when used like this can tell when the end of the arrays are, so it's possible to overrun the buffers. You can fix that by using fgets and specifying a field width:

Code:

#include <stdio.h>

int main(void)
{
  char inEmail[500];
  char inName[500];
  char inMessage[150];
  char exitKey;

  printf("Enter a greeting message: ");
  fgets(inMessage, sizeof inMessage, stdin);

  printf("Enter a name please: ");
  scanf("%499s",inName);

  printf("Enter your email address: ");
  scanf("%499s",inEmail);

  printf("%s\n",inMessage);
  printf("Your name is %s\n",inName);
  printf("Your email address is %s\n",inEmail);

  printf("Press return to exit program:");
  scanf("%c",&exitKey);
  getchar();

  return 0;
}

It's also a good idea to test input for success. Anything that comes from outside of your program should be viciously validated.

So here is my revised code using fgets :

That's not any better. You use fgets, but still give a size bigger than the buffer for inMessage.

fgets() also adds a newline to the end of your input string, something you might have to deal with.

Code:

// secure string input, fgets() replaces gets() and scanf()

#include <stdio.h>   // BUFSIZ usually 512
#include <string.h> 

int main()
{
  char buf[BUFSIZ] = "";
  char *p;
  
  printf("Please enter a line of text (max %d characters)\n", sizeof(buf));
  
  if (fgets(buf, sizeof(buf), stdin) != NULL)
  {
    // remove trailing \n 
    if ((p = strchr(buf, '\n')) != NULL)
      *p = '\0';
    printf("you entered: %s\n", buf);      
  }

  getchar();  // wait  
  return 0;
}

You are absolutely hairsplitting right Kermit. In this case there will be most likely a newline in the string, unless your name is 500 characters long.

Glad you brought it up! I am the same way, just don't want to admit it!

In this case there will be most likely a newline in the string, unless your name is 500 characters long.

Wacky input happens. What if someone wants to play a joke and redirects stdin to a file? I say it's better to test than to get caught out in the rain, and in my experience, 'exceptional' doesn't mean 'uncommon'.