Problem with a little piece of code in C

FFX · 11-13-2021, 11:14 AM

Hi,

I am new to C programming and I came across a problem. When I comiple and run the following code I get the output: You have entered +:

Code:

#include <stdio.h>

int main(int argc, char *argv[])
{


if ((*argv[1]) == '+'){


    printf("You have entered +");

}


    return 0;
}

But when I compile and run the following code I get not output at all:

Code:

#include <stdio.h>

int main(int argc, char *argv[])
{


if ((*argv[1]) == '*'){


    printf("You have entered *");

}


    return 0;
}

So what is the problem and how can I dissolve this?

Thanks.

Ben

astrogeek · 11-13-2021, 11:53 AM

Welcome to the Programming forum!

The problem is that when you enter '*' the shell expands that before it is sent to the program, so that *argv[1] is not a literal '*' but is the first value resulting from the expansion and the test fails.

To see what is actually there you might try adding an else clause to show the actual value pointed by argv[1] on failure.

When writing code and some test does not produce the expected result, a good first step for troubleshooting is to write in a way to see what the actual test parameters are when the program runs. Sometimes you may want to place that immediately before the test, and sometimes after or as an alternate when the test fails as I have suggested.

Good luck with your C programming!

FFX · 11-14-2021, 06:31 AM

Quote:

Originally Posted by astrogeek

Welcome to the Programming forum!

Thanks, and thanks for the help.

Ben

SamHobbs · 12-06-2021, 01:41 AM

When I execute:

Code:

if ((*argv[1]) == '+') {
	printf("You have entered +");

I get an access violation. And that makes sense because I did not provide an argument so there is nothing there to be accessed. It is instead trying to look at memory location zero. The fact that your code does not get an access violation is near proof that you are providing an argument somehow. We do not know what the argument is so the suggestion to see what is actually there was probably very helpful. If so then you should give credit for the help.

FFX · 12-06-2021, 07:13 AM

Hi Sam,

My explanation was not complete. I did provide + as the first argument on the command line.
The same counts for the second code but then I provided *

Ben