Go4Expert - UNKNOWN! runtime error

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UNKNOWN! runtime error

Code:

#include<stdio.h>



void reverse(char str[]);



int main()

{

    char str[100];

    int i;



    printf("Enter to reverse : ");

    scanf("%s",str);

    reverse(str);

    return(0);

}

/* Function */



void reverse(char str[])

{



    int i;

    for(i=99;i>=0;i--)

    {

        printf("%c",str[i]);

    }

    putchar('\n');

}

:embarasse:embarasse:embarasse:embarasse:embarasse :embarasse:embarasse:embarasse:embarasse:embarasse :embarasse:embarasse\

Why there is a runtime error in the above programme..........

help!!!!!!
URJENT!!!!!!!!

Re: UNKNOWN! runtime error

Code:

#include<stdio.h>

#include <string.h>



void reverse(char str[]);



int main()

{

    char str[100];

    int i;



    printf("Enter to reverse : ");

    scanf("%s",str);

    reverse(str);

    return(0);

}

/* Function */



void reverse(char str[])

{



    int i;

    int z=strlen(str);

    for(i=z-1;i>=0;i--)

    {

        printf("%c",str[i]);

    }

    putchar('\n');

}

the error is that you reserve 100 positions in memory for the string entered
but it uses actually only those the user enter.

so if i enter the word car-->'c' 'a' 'r' '\0' so it uses 4 positions instead of 100
so instead of starting from the end of 100positions you must start from the end of 4positions down to 0

Re: UNKNOWN! runtime error

That doesn't explain why there would be a runtime error. It would explain why garbage is displayed and if I modify the program to add

Code:

        for (i=0; i<100; i++)

                str[i]='~';

to main just after the int i declaration, the output is:
Enter to reverse : hello
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ olleh

but even without this modification I don't get a runtime error (in Visual Studio 2008 building the program in Debug mode).

When it prompted you to enter a string, did you enter more than 100 characters? That might cause a runtime error - this is the infamous "buffer overflow" bug.

If not then I can only suggest this is a compiler bug. Maybe the RTL has a problem with %c for non-printable characters. You can test this hypothesis with a simple program:

Code:

printf("Starting test\n");

fflush(stdout);

for (i=0; i<256; i++)

{

  printf("%d %c ",i,i);

  fflush(stdout);

}

The fflush ensures that the last character before the runtime error is displayed; normally output is buffered which can cause confusion when a program crashes - it looks like it crashed before it actually went tits up.