Saving to a file and checking a string for a letter (in C)

I was wondering how I would go about checking the first letter entered into a string variable could be checked.

As can be seen in this block of code

fflush(stdin);
printf("\n\nEnter statement #d", ctr);
gets(statement);
while ((statement != "Q") | | (statement != "q"));
{
fputs(statement, fp);
ctr+=1;
fflush(stdin);
printf("\n\nEnter statement #%d",ctr);
printf("\n(Enter only Q or q to exit)\n");
gets(statement);
}

I am able to enter a text string, but am unable to compare it with the letters "Q" or "q".

I'm also having a problem with writing to the text file which is indicated by the pointer fp. What is it I may be doing wrong?

Here's part of your answer:
The reason you can't check q or Q is because you are using a while-loop, where the condition to end your loop gets checked PRIOR to executing the code inside the loop. Try using a DO loop here instead.

no stevetabler, he gets() befor the loop, so the condition is checked properly. a While loop will work fine. It's been a while since i've done C, but I think your problem is that gets() grabs the whole line, including the newline (/n). try storing Q or q in a string, and use the string compare function (strcmp i think). Ya it's been a while, i could be wrong.

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Come, son of jor-el, kneel before zod! Snootchy Bootchies!

Get rid of the OR | | and use AND && instead. Your while loop never exits since your OR statement always returns true, unless statement could be 'Q' and 'q' at the same time, which of course is impossibe.

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"Log, its better than bad, its good!"



[This message has been edited by Begby (edited December 05, 2001).]

blah begby got it. didn't see that, i hate programing. hrmph.

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Come, son of jor-el, kneel before zod! Snootchy Bootchies!

Thanks to everyone!!!

It turned out to be two things.

1) Using strcmp, I was able to check the values of the first two letters of the string against the values returned by Q and then by q. This solved the problem on how to evaluate.

2) That use of && instead of | | was exactly what I was looking for. As Begby pointed out, that loop was locked because there was no way that the values returned could ever satisfy that origianl condition.

I also learned something to pass on to other beginnig C programmers concering fprintf---fprintf will _only_ write to the output device when fclose is invoked.

Again, thanks for the help from stevetabler,
the_real_oldie, and Begby

Quote:

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Originally posted by Pupalaikis:

I also learned something to pass on to other beginnig C programmers concering fprintf---fprintf will _only_ write to the output device when fclose is invoked.

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This is a bufferring problem common to most languages. Not sure about C, but Tcl and a few others allow you to set the buffer to 0 or at least very small so that the write is done when the small buffer is full rather than when the file is closed.

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The price of freedom is high.

Quote:

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1) Using strcmp, I was able to check the values of the first two letters of the string against the values returned by Q and then by q. This solved the problem on how to evaluate.

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I'm not sure what type of variable your string was, but there's an easier (and faster) way to check against a single character.

First of all, "Q" is a string literal, while 'Q' would represent a character. Here's the difference:

char a[10] = "Q";
char b[10] = 'Q';

The first statement copies a Q character AND a null character into the first two chars of a. I don't think the second will even compile, but if it did, it would only assign the character Q to the first char of b. I'm not even sure what the conditional statement

if (a == "Q")

would do. Probably something goofy, if it compiles https://www.sharkyforums.com/images/.../2005/06/5.gif

The "correct" way to check to see if the first char of *a is a Q would be:

if ((a[0] == 'Q') | | (a[0] == 'q'))

I prefer using toupper:

if (toupper(a[0]) == 'Q')

Now, if you want to distinguish between a user entering "Q" and "Quasimodo," you'll need to do a check like:

if ((toupper(a[0]) == 'Q') && (a[1] == 0))

Of course, in this case the strcmp you used will work, too:

if (!strcmp(a, "Q"))