How can I make my app exit...

This is a discussion on How can I make my app exit... within the C Programming forums, part of the General Programming Boards category; Hey, this is probably a simple thing to do. Basically, i'm doing a project for uni work. it is just ...

  1. #1
    kie
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    Question How can I make my app exit...

    Hey, this is probably a simple thing to do. Basically, i'm doing a project for uni work. it is just a simple currency converter. I have managed to get the application so the data is checked and if it is not numercial, the user is alerted. But I would also like the program to exit when the user types exit.

    Here is what I have so far

    Code:
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    void welcome(void); //displays welcome message and app info
    void convert(void); //converts users input to $
    int main()
    {
    	int count;
       welcome();
       count=0;
       while (count==0)
          {
    		convert();
          }
    }
    void welcome(void)  //this bit welcomes the user and shows some info
    {
    	printf ("Currency Converter\nBy Kieran Symes\n24/10/2006\n");
    }
    void convert(void)
    {
    	char line[80];
    	double input;  //users input
    	char *endptr;
    	int valid = 0;  //decides whether data is valid, this may not be required...
       double output; //output after calcs
    	do
       {
    		printf("\nPlease enter an amount you wish to convert without the &#163;.\n");
    		fgets(line, 80, stdin);  //get data
    		input = strtod(line, &endptr);
    		if (endptr == line)
    		{
    			printf("\nYou have entered incorrect data.  Please ensure you type numbers only!\n\n");
    			valid = 0;
    		}
    		else
    		{
    			valid = 1;
    		}
    	   } while (!valid);  //data is valid
         	output = input * 1.49;  //do the maths
       	printf("\n\&#163;%.2f is equal to %.2f euros.\n", input, output);  //print output
    }
    I think I can use strcmp but I am unsure how to use this correctly. If anybody would like to post an example with sample code, I would very much appreciate it. Also, where would I put this?

    I am quite new to programming so that is why my code may not be very efficient etc.

    thanks
    Last edited by kie; 11-01-2006 at 03:03 PM.

  2. #2
    Registered User whiteflags's Avatar
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    You should ask yourself, how can you update the count variable if you don't pass it's address to convert? You're stuck in an infinite loop for this reason.

    At a minimum you should do something like
    Code:
    void convert( int *count );
    
    /* ... */
    
    int count = 0;
    welcome();
    while ( count == 0 )
    {
       convert(&count);
    }
    and handle count accordingly for however long you want the program to run.

  3. #3
    MFC killed my cat! manutd's Avatar
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    Try this:
    Code:
    if (line == "exit") //And yes, this should take uppercase;i'm lazy
    {
         printf("Exiting...");
         return 0;
    }
    Silence is better than unmeaning words.
    - Pythagoras
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  4. #4
    Registered User whiteflags's Avatar
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    Even if his program was working that way, it wouldn't matter because comparing string literals and character arrays with == gives incorrect results: You're actually comparing the pointer to string s == t. And it will always be wrong. This is because string literals are stored in anonymous read only memory which will never point to the same place as a character array.

  5. #5
    kie
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    hey manutd, I gave that a try and if you type exit, nothing happens, it just proceeds to the Enter an amount to convert part.

    this is the sort of method I was planning on using. so if anybody else can think of getting this method to work, I would appreciate any help

  6. #6
    MFC killed my cat! manutd's Avatar
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    What OS are you using?
    Silence is better than unmeaning words.
    - Pythagoras
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  7. #7
    Registered User whiteflags's Avatar
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    > this is the sort of method I was planning on using.
    Then you have to rewrite your loop in main. Try implementing a case-insensitive strcmp() to do the work: break the loop when the comparison is true. And then look here.

  8. #8
    kie
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    I would like to get around this problem without changing code if I can, I am using Windows XP MCE

  9. #9
    MFC killed my cat! manutd's Avatar
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    If you return a number it should kill you app (as main is a function, returning a value ends the function).
    Silence is better than unmeaning words.
    - Pythagoras
    My blog

  10. #10
    kie
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    when i compile, i get the error "convert() can not return a number"

  11. #11
    Reverse Engineer maxorator's Avatar
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    Ofcourse you are. Replace this:
    Code:
    if (line == "exit") //And yes, this should take uppercase;i'm lazy
    {
         printf("Exiting...");
         return 0;
    }
    with this:
    Code:
    if (line == "exit") //And yes, this should take uppercase;i'm lazy
    {
         printf("Exiting...");
         return;
    }
    And try to understand these simple errors next time.
    "The Internet treats censorship as damage and routes around it." - John Gilmore

  12. #12
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    I'm still a bit fuzzy on the whole comparing strings with == thing. . . I really don't think that will work the way you expect it to. . .

    Actually, I know that it will NOT work in C. maxorator, why do you keep using this, especially when citizen in post #4 has already stated that this DOES NOT WORK? Don't you read the entire thread before posting?

    If you are comparing strings you could use something like strcmp() or strncmp(). A simple == is not for char *'s or string literals. If you compare a char * to a string literal, and you have not assigned the string literal to the char *, you will ALWAYS get false.

  13. #13
    Reverse Engineer maxorator's Avatar
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    Whoops, I copied the code.
    Code:
    if (strcmp(line,"exit")==0) //And yes, this should take uppercase;i'm lazy
    {
         printf("Exiting...");
         return;
    }
    I just meant that he probably had that "return 0;" in where it supposed to be just "return;".
    "The Internet treats censorship as damage and routes around it." - John Gilmore

  14. #14
    kie
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    it still seems to ignore that and just asks for another value stating that invalid data was entered

  15. #15
    Reverse Engineer maxorator's Avatar
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    Post your new code.
    "The Internet treats censorship as damage and routes around it." - John Gilmore

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