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Unexpected string output
hey i m using code::blocks for c programming and when i run the code, it stops in the middle.
When i take help of debugger in below code it shows ..
a syntax error in expression near "if"..
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The debugger raised a syntax error? Not the compiler? That's a first for me in my decades of experience. BTW, compiling that with gcc and all warnings on compiled clean.
Is your input string what you expect it to be? Your input code looks like it's only inputting every other character:
Code:
while(getchar()!='\t')
{
printf("entered while loop.Iteration no. %d \n",i);
s1[i]=getchar();
i++;
printf("Iteration no. %d & s1 char is: %c \n",i,s1[i]);
}
That second printf also doesn't look right, since you're displaying a character in s1 that you haven't written to yet. For example, the first character goes into s1[0], but then you increment i before echoing it out, so you are in fact "echoing" out s1[1], which, since you have not yet written anything there, contains whatever garbage is there. My recommendation is that the i++; should be moved to the end of the loop. Or replace the while with a for.
When your output doesn't look right, one of the first things to check is whether your input is right.
Last edited by dwise1_aol : February 4th, 2013 at 10:38 AM.
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@dwise God you are so right abt the increment i before echoing it out,damn silly mistakes.
And thanks a lot about that "Skipping" issue!
That solves everything.
And yea man im nice with the compiler cut lose sm slack man.
Quote:
Is your input string what you expect it to be? Your input code looks like it's only inputting every other character
Q: Why is I/p string I/putting every other character???
Quote:
Originally Posted by dwise1_aol
The debugger raised a syntax error? Not the compiler? That's a first for me in my decades of experience. BTW, compiling that with gcc and all warnings on compiled clean.
Is your input string what you expect it to be? Your input code looks like it's only inputting every other character:
Code:
while(getchar()!='\t')
{
printf("entered while loop.Iteration no. %d \n",i);
s1[i]=getchar();
i++;
printf("Iteration no. %d & s1 char is: %c \n",i,s1[i]);
}
That second printf also doesn't look right, since you're displaying a character in s1 that you haven't written to yet. For example, the first character goes into s1[0], but then you increment i before echoing it out, so you are in fact "echoing" out s1[1], which, since you have not yet written anything there, contains whatever garbage is there. My recommendation is that the i++; should be moved to the end of the loop. Or replace the while with a for.
When your output doesn't look right, one of the first things to check is whether your input is right.
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Quote:
Originally Posted by lovecodecakes
@dwise God you are so right abt the increment i before echoing it out,damn silly mistakes.
And thanks a lot about that "Skipping" issue!
That solves everything.
And yea man im nice with the compiler cut lose sm slack man.
Q: Why is I/p string I/putting every other character???
because you have used getchar()... it takes only 1 char input at a time...
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Quote:
Originally Posted by lovecodecakes
Q: Why is I/p string I/putting every other character???
Because your loop has two calls to getchar(), only the return value from one of which was assigned to the string, the other being discared after checking for TAB.
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Quote:
Originally Posted by lovecodecakes
And yea man im nice with the compiler cut lose sm slack man.
I don't know what you're talking about here.
Quote:
Originally Posted by lovecodecakes
Q: Why is I/p string I/putting every other character???
Because you're calling getchar() twice for every character you actually save as input. First you get a character to test it for being a tab. Then you get the next character to place into s1. Then you get the third character to test whether it's a tab. Then you get the fourth character place into s1 -- at this point, you have processed four characters from the input buffer and have only placed two of them into s1.
Take a look at my suggested code. In while, you getchar a character and assign it to a char variable, thus saving it for use. Then in the same while, you test that char for not being a tab; remember that the value of an assignment expression is the value being assigned! Then within the body of the while loop when you insert that character into the s1 array, you do still have that character because you had saved it in that char variable. And this is just one of a number of approaches you could have taken.
Sometimes, a very good debugging technique is to take paper and pencil in hand and play computer. Go through your program step-by-step and do everything that it tells you to do, keeping track of variable values on the paper. In your case, you should fill the input buffer with the string of characters that you intend to type in and keep track of which character each and every call to getchar() "eats" and which character will then be the next to be "eaten".
One big problem that programmers have is the same that writers have: when we read our own code we almost never see what we have actually written, but rather what we "see" what we remember intending to have written. One solution is to have somebody else have a look, much like a writer will have somebody else proofread their work. Usually that different set of eyes will see an error jump right out of them, one that we were ourselves blind to. Or that other person have questions about something that we had thought we had taken care of but hadn't yet. Another solution for when ours is the only set of eyes available is to read through our program painstakingly paying attention to each detail. One way of doing this is to play computer with pencil and paper. Another way is to sit down with somebody else and walk them through our program explaining exactly what it is doing; this forces you to think through each line enough to be able to explain it, whereupon your obvious mistake will suddenly become apparent to you.
It's a very common problem that we all have been through and continue to have to deal with.
Last edited by dwise1_aol : February 4th, 2013 at 02:54 PM.
Posts: 14
Time spent in forums: 2 h 41 m 47 sec
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Thanks yea I edited my code & its up and running. Thanks for the advice on proofreading.Skipped on reading twice from I/p.
Quote:
Originally Posted by dwise1_aol
I don't know what you're talking about here.
Because you're calling getchar() twice for every character you actually save as input. First you get a character to test it for being a tab. Then you get the next character to place into s1. Then you get the third character to test whether it's a tab. Then you get the fourth character place into s1 -- at this point, you have processed four characters from the input buffer and have only placed two of them into s1.
Take a look at my suggested code. In while, you getchar a character and assign it to a char variable, thus saving it for use. Then in the same while, you test that char for not being a tab; remember that the value of an assignment expression is the value being assigned! Then within the body of the while loop when you insert that character into the s1 array, you do still have that character because you had saved it in that char variable. And this is just one of a number of approaches you could have taken.
Sometimes, a very good debugging technique is to take paper and pencil in hand and play computer. Go through your program step-by-step and do everything that it tells you to do, keeping track of variable values on the paper. In your case, you should fill the input buffer with the string of characters that you intend to type in and keep track of which character each and every call to getchar() "eats" and which character will then be the next to be "eaten".
One big problem that programmers have is the same that writers have: when we read our own code we almost never see what we have actually written, but rather what we "see" what we remember intending to have written. One solution is to have somebody else have a look, much like a writer will have somebody else proofread their work. Usually that different set of eyes will see an error jump right out of them, one that we were ourselves blind to. Or that other person have questions about something that we had thought we had taken care of but hadn't yet. Another solution for when ours is the only set of eyes available is to read through our program painstakingly paying attention to each detail. One way of doing this is to play computer with pencil and paper. Another way is to sit down with somebody else and walk them through our program explaining exactly what it is doing; this forces you to think through each line enough to be able to explain it, whereupon your obvious mistake will suddenly become apparent to you.
It's a very common problem that we all have been through and continue to have to deal with.
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