Newbie college student :)

This is a discussion on Newbie college student :) within the C Programming forums, part of the General Programming Boards category; Hi guys, I am learning C. And made a program and it's giving me Segmentation fault when I run it ...

  1. #1
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    Newbie college student :)

    Hi guys,

    I am learning C. And made a program and it's giving me Segmentation fault when I run it . Please I need help. I run it under munro unix. Can anyone tell me what am I doing wrong.

    Code:
    #include <stdio.h>
    
    #define A 100
    #define B 90
    #define C 80
    #define D 70
    #define E 60
    #define ZERO 0
    
    int main()
    
    {
    
    char ch;
    char firstname, lastname;
    char low=3;
    char high=12;
    int mark=0, n=0;
    
    int randNumber;
    
    srand(time(0));
    
    randNumber=rand() % 10 + 3;
    
    printf("The number of students in the class is %d.\n", randNumber);
    
    while (n != randNumber)
    {
    
    
    n++;
    printf ("Please enter your first name: \n");
    scanf ("%s", &firstname);
    fflush(stdin);
    printf ("Please enter your last name: \n");
    scanf ("%s", &lastname);
    fflush(stdin);
    printf ("Please enter your marks: \n");
    scanf ("%d", &mark);
    fflush(stdin);
    
    if (mark >= B || mark <= A)
    
    printf("%s %s %d Grade A\n", firstname, lastname, mark);
    
    
    else if (mark >= C || mark <= B)
    
    
    printf("%s %s %d Grade B\n", firstname, lastname, mark);
    
    
    else if (mark >= D || mark <= C)
    
    
    printf("%s %s %d Grade C\n", firstname, lastname, mark);
    
    
    else if (mark >= E)
    
    
    printf("%s %s %d Grade D\n", firstname, lastname, mark);
    
    
    else if (mark < E)
    
    
    printf("%s %s %d Grade F\n", firstname, lastname, mark);
    
    
    else
    
    printf("Marks are invalid./n");
    
    return 0;
    
    }
    }
    Thanks a lot guys...

  2. #2
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    Try this you still need to modify a few things like taking the \n out of the string firstname and lastname and not use fflush to clear the stdin buffer

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>
    
    #define A 100
    #define B 90
    #define C 80
    #define D 70
    #define E 60
    #define ZERO 0
    
    int main()
    {
    
    	/*char ch;*/
    	char firstname[80], lastname[80];
    	/*char low=3;
    	char high=12;*/
    	int mark=0, n=0;
    
    	int randNumber;
    
    	srand(time(0));
    
    	randNumber=rand() % 10 + 3;
    
    	printf("The number of students in the class is %d.\n", randNumber);
    
    	while (n != randNumber)
    	{
    		n++;
    		printf ("Please enter your first name: \n");
    		fgets(firstname, sizeof firstname, stdin);
    		fflush(stdin);
    		printf ("Please enter your last name: \n");
    		fgets(lastname, sizeof lastname, stdin);
    		fflush(stdin);
    		printf ("Please enter your marks: \n");
    		scanf ("%d", &mark);
    		fflush(stdin);
    
    		if (mark >= B && mark <= A)
    			printf("%s %s %d Grade A\n", firstname, lastname, mark);
    		else if (mark >= C && mark <= B)
    			printf("%s %s %d Grade B\n", firstname, lastname, mark);
    		else if (mark >= D && mark <= C)
    			printf("%s %s %d Grade C\n", firstname, lastname, mark);
    		else if (mark >= E)
    			printf("%s %s %d Grade D\n", firstname, lastname, mark);
    		else if (mark < E)
    			printf("%s %s %d Grade F\n", firstname, lastname, mark);
    		else
    			printf("Marks are invalid./n");
    	}
    	
    	return 0;
    }
    [edit]
    Your logic was out too you use || instead of && its now changed
    [/edit]
    Last edited by gsoft; 01-22-2005 at 05:15 PM.

  3. #3
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    ok let me try that. Thanks

  4. #4
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    No it doesn't work . It giving me different errors now. When I compile it.

    Code:
    test5.c:1: syntax error before '<' token
    In file included from test5.c:2:
    /usr/include/stdlib.h:137: syntax error before "__ctype_get_mb_cur_max"
    In file included from /usr/include/sys/types.h:266,
                     from /usr/include/stdlib.h:416,
                     from test5.c:2:
    /usr/include/bits/pthreadtypes.h:48: syntax error before "size_t"
    /usr/include/bits/pthreadtypes.h:51: syntax error before "__stacksize"
    In file included from test5.c:2:
    /usr/include/stdlib.h:433: syntax error before "size_t"
    /usr/include/stdlib.h:462: syntax error before "size_t"
    /usr/include/stdlib.h:556: syntax error before "__size"
    /usr/include/stdlib.h:558: syntax error before "__nmemb"
    /usr/include/stdlib.h:567: syntax error before "size_t"
    In file included from /usr/include/stdlib.h:578,
                     from test5.c:2:
    /usr/include/alloca.h:33: syntax error before "__size"
    In file included from test5.c:2:
    /usr/include/stdlib.h:583: syntax error before "__size"
    /usr/include/stdlib.h:739: syntax error before "size_t"
    /usr/include/stdlib.h:743: syntax error before "size_t"
    /usr/include/stdlib.h:812: syntax error before "size_t"
    /usr/include/stdlib.h:815: syntax error before "size_t"
    /usr/include/stdlib.h:819: syntax error before "size_t"
    /usr/include/stdlib.h:822: syntax error before "size_t"
    /usr/include/stdlib.h:830: syntax error before "size_t"
    /usr/include/stdlib.h:834: syntax error before "size_t"
    /usr/include/stdlib.h:841: syntax error before "mbstowcs"
    /usr/include/stdlib.h:842: syntax error before "size_t"
    /usr/include/stdlib.h:844: syntax error before "wcstombs"
    /usr/include/stdlib.h:845: syntax error before "size_t"
    In file included from test5.c:3:
    /usr/include/time.h:197: syntax error before "strftime"
    /usr/include/time.h:197: syntax error before "size_t"
    test5.c: In function `main':
    test5.c:33: `stdin' undeclared (first use in this function)
    test5.c:33: (Each undeclared identifier is reported only once
    test5.c:33: for each function it appears in.)

  5. #5
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    oh sorry hold my fault I forgot to put #include at the top, Please wait let me run it again

    sorry

  6. #6
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    It's working now . Thanks...Just one question, fgets is better then scanf()?. Teacher was telling me to use scanf(). we are not allowed to use fgets () right now.

    thanks

  7. #7
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    Gsoft,

    I tried scanf() in place of fgets() and it's working fine.

    Thanks

  8. #8
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    scanf allows you to go over the allocated buffer something I dont think you should do. Scanf() is good but I wouldnt use it for strings.

  9. #9
    ... kermit's Avatar
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    scanf() is not the function of choice for a many C programmers. It just opens a can of very stinky worms. If you must use it, remember that it returns a value, which corresponds to the amount of items correctly converted. This allows a small measure of error checking. For example:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
        int age;
        char fname[10];
    
        printf("Enter your first name: ");
        fflush(stdout);
        if (scanf("%s", fname) != 1) {
            puts("scanf() error!");
            exit(EXIT_FAILURE);
        }
        printf("Enter your age: ");
        fflush(stdout);
        if (scanf("%d", &age) != 1) {
            puts("scanf() error!");
            exit(EXIT_FAILURE);
        }
        printf("Your first name is %s, and your age %d\n", fname, age);
        return 0;
    }
    ~/
    Last edited by kermit; 01-22-2005 at 05:51 PM.

  10. #10
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    kermit,

    so if "fname" is not equal to "1" it will exit?. So what does the vaule "1" stand for?. Sorry I am new to this, so trying to understand the code that you wrote .

    Thanks

  11. #11
    Registered User Sake's Avatar
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    >>So what does the vaule "1" stand for?
    scanf returns the number of items successfully converted. Because the call is only converting one item, a successful return would be 1.

  12. #12
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    Ahhh, ok.... Thanks

  13. #13
    ... kermit's Avatar
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    Quote Originally Posted by jat421
    kermit,

    so if "fname" is not equal to "1" it will exit?. So what does the vaule "1" stand for?. Sorry I am new to this, so trying to understand the code that you wrote .

    Thanks
    As Sake pointed out, the value 1 corresponds to the amount of arguments successfully converted by scanf().

    Many functions return a value, which are free to be used, or ignored. A good example of an ignored return value would be the one returned from the printf() function - printf() returns the amount of characters printed, yet you will probably not see that value used very often. In the case of scanf(), as has been mentioned, we can choose to ignore or not ignore its return value, and instead use it to see if there was any problem with conversion.

    Now consider how the return value from scanf() is obtained. When you call a function which returns a value, you can assign it to a variable like so:

    Code:
    int ret_val;  /* will hold whatever value scanf() returns */
    ret_val = scanf("%s", fname);
    To see if scanf() was successful, you would check the value stored in the variable ret_val against the number of arguments passed to scanf() (which in this case is 1):

    Code:
    int ret_val;
    ret_val = scanf("%s", fname);
    if(ret_val != 1) {
    /* do some stuff */
    }
    Of course, writing code in the last method is awkward at best. Not much sense in declaring an extra variable if its not necessary.

    Now then, if you had a call to scanf() that passed 2 arguments, you would check to see that the return value of scanf() equalled 2. Any number other than 2, indicates a problem. For example:

    Code:
    char fname[10];
    char lname[10];
    
        printf("Enter your first and last name: ");
        fflush(stdout);
        if (scanf("%s%s", fname, lname) != 2) {
            puts("scanf() error!");
            exit(EXIT_FAILURE);
        }
    Finally, in the examples I have given, if scanf() fails, for whatever reason, the program exits.

    ~/
    Last edited by kermit; 01-22-2005 at 07:13 PM.

  14. #14
    Just Lurking Dave_Sinkula's Avatar
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    Code:
    char fname[10];
    char lname[10];
    
        printf("Enter your first and last name: ");
        fflush(stdout);
        if (scanf("%s%s", fname, lname) != 2) {
            puts("scanf() error!");
            exit(EXIT_FAILURE);
        }
    Never use scanf's %s directive without supplying width. Otherwise you've created something similar to gets.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  15. #15
    ... kermit's Avatar
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    You know its funny Dave, I was just thinking about people who know how to use scanf() better than me, and you came to mind. Of course using scanf() like that is a lovely way to over run the bounds of an array, and I should have mentioned it.
    Last edited by kermit; 01-22-2005 at 08:22 PM.

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