Why my code crashes

Hi, I need the user to enter coordinates x,y . The x needs to go in front of the number like so : x8.2 . My code works , but it accepts x8.2 just the same as 8.2x. This is not allowed to happen ie . it must reject the point if it sees the x at the end . Here is what I came up with :

Code:

---


#include <stdio.h>
int main(void)

{

FILE * output = stdout;
FILE * input = stdin;

char stringValue[8];
float value;
fscanf(input, "%s", stringValue);

// check last character
if (stringValue[ strlen( stringValue ) - 1] == 'x')

{
        fprintf(output,"You have entered incorrect value - put the x at the front !");// wrong value
        return 0;
}

else

{
        fscanf(input, "%f", value);
        fprintf(output,"The program will continue");
}

}

---

I run that , it works for any number with x at the end , it says incorrect put at x at front , but if a correct number is putin, it will crash ? If Im not doing this correctly can you show me the right way ?
Thank you

Im an idiot it crashes because I forgot the &value , instead of just value .

Maybe someone can help me with another problem when I try to compare strings using strcmp() I get a segmentation fault . Here is an exampl of what I mean :

Code:

---

#include <stdio.h>

#include <string.h>


int main()

{
char *name = "EDDIE";
char *guess;
int correct = 0;

printf("Enter a name in uppercase: ");

while(!correct)

{
        fgets(guess ,10, stdin);

        if(strcmp(name, guess)==0)
{
        printf("Correct!\n");
                correct = 1;
}       

   
else

{
        printf("Try again: ");
}


}

return 0;

}

---

I appreciate your help :)

guess needs to be a sufficiently big array, not a pointer. You're writing into memory that you don't own.

Edit: Also,
1) Way too much white space.
2) Please fix your indentation.
3) You don't need the variable correct. Just use an infinite loop and use "break;" to get out when done.

Quote:

---

Originally Posted by robatino

guess needs to be a sufficiently big array, not a pointer. You're writing into memory that you don't own.

Edit: Also,
1) Way too much white space.
2) Please fix your indentation.
3) You don't need the variable correct. Just use an infinite loop and use "break;" to get out when done.

---

Thanks , just to clarify do you mean I should use char guess[#] ? Sorry if my questions sound dumb but I am just a beginner . I don't know much about indenting , but hopefully it now looks better. Thanks
/Edit just did a bit of research maybe something like :
int guess[] = {"EDDIE"};

Since you're telling fgets() to read at most 10 characters (including the final null character), you need to allocate at least that many, so you should use

Code:

---

char guess[10];

---

>Do you mean I should use char guess[#] ?
Yes. The way you have guess declared:

Code:

---

char *guess;

---

guess is a pointer to char. In order to use a pointer, first you must allocate some memory for it using a function such as malloc(). Or simply declare guess as an array of char, as you show above.

Ok I am now using

Code:

---

char guess[10]

---

However no matter what I put in it says Try again . This includes if i enter EDDIE and "EDDIE". Any idea why it's doing this ? ( Ichanged the code posted before to show what I did )

I have also tried changing the code to this :

Code:

---

int name[] = {"EDDIE"};
char guess[10];
int correct = 0;

---

But I highly doubt that the second method can work .
Thanks for your time

Quote:

---

Originally Posted by ICool

However no matter what I put in it says Try again . This includes if i enter EDDIE and "EDDIE". Any idea why it's doing this ?

---

fgets leaves the terminating '\n' at the end of the returned string.
one way to get rid of that is

Code:

---

        char *p;
        p = strchr(guess, '\n');
        if ( p )
            *p = 0;

---

Kurt

As said before, it is the '\n' char which is playing your problem. Remove the \n char and replace that with the '\0' char. Beforem you compare the two string.

That should work. And work along your code indendation.

ssharish2005

Quote:

---

Originally Posted by ZuK

fgets leaves the terminating '\n' at the end of the returned string.
one way to get rid of that is

Code:

---

        char *p;
        p = strchr(guess, '\n');
        if ( p )
            *p = 0;

---

Kurt

---

Can you please clarify what you mean . How would I implement the above code . This compiles but crashes :

Code:

---

printf("Enter a name in uppercase: ");
char *p;
p = strchr(guess, '\n');
if ( p )
*p = 0;

while(!correct)

---

Code:

---

#include <stdio.h>
#include <string.h>

int main()  {
    char *name = "EDDIE";
    char guess[10];
    int correct = 0;
    char * p;

    printf("Enter a name in uppercase: ");

    while(!correct) {
        fgets(guess ,10, stdin);
        p = strchr(guess, '\n');
        if ( p )
            *p = 0;
           
        if(strcmp(name, guess)==0) {
            printf("Correct!\n");
            correct = 1;
        }         
        else  {
            printf("Try again: ");
        }
    }
}

---

kurt

Thank you so much . That works perfectly :)

Is this how I would do the same but for more than 1 name ?

Code:

---

#include <stdio.h>
#include <string.h>

int main() {
int name[] = {"EDDIE","BEN","DAVE"};

char guess[10];
int correct = 0;
char * p;

printf("Enter a name in uppercase: ");

while(!correct) {
fgets(guess ,10, stdin);
p = strchr(guess, '\n');
if ( p )
*p = 0;

if(strcmp(name, guess)==0) {
printf("Correct!\n");
correct = 1;
}
else {
printf("Try again: ");
}
}
}

---

does it compile ?

Kurt

No :(

I get this error when it tries to coimpile it :

Code:

---

strings.c(5) : Error: need explicit cast to convert
from: char *
to  : int
        if(strcmp(name, guess)==0) {
                            ^
strings.c(19) : Error: need explicit cast for function parameter 1 to get
from: int *
to  : char const *
--- errorlevel 1

---

Code:

---

int name[] = {"EDDIE","BEN","DAVE"};

---

U are comparing with the int array which is not right. Perhaps it should have been a 2D string. And even more the strcmp string is expecting the char * not int * or char[][].

So above code should be

Code:

---

char name[][20] =  {"EDDIE","BEN","DAVE"};

---

And perhaps you now should change your code to suite he above statment

Code:

---

#include <stdio.h>
#include <string.h>

int main()
{
   
 char name[][20] = {"EDDIE","BEN","DAVE"};
 int i;
 char guess[10];
 int correct = 0;
 char * p;

 printf("Enter a name in uppercase: ");

 while(!correct)
 {
  fgets(guess ,10, stdin);
  p = strchr(guess, '\n');
  if ( p )
    *p = 0;

 for(i=0;i<3;i++)
 {
  if(strcmp(name[i], guess)==0)
  {
  printf("Correct!\n");
  correct = 1;
  getchar();
  return 0;
  }
 }
 printf("Try again: ");
 }
 getchar();
 return 0;
}

---

ssharish2005

The compiler tries to tell you that a pointer to an int is not a c-string.
You could try to declare name like this

Code:

---

char name[][6] = {"EDDIE","BEN","DAVE"};

---

Of corse you would need some kind of loop to find out if any of the names matches.
Kurt

ssharish and kurt , thank you VERY much . That solves my problem perfectly :)