Unexpected output from function

Question

I was writing a function for finding character from a given string:

Test.c file is as follows:

#include<stdio.h>

int findIndex(char *array, char search)
{
    int count=0;
    char test;
    int check = 0, repeat;

    if(search == ',')
        repeat = rand()%10;

    else
        repeat = rand()%11;

    while((test = array[count]) != NULL)
    {
        if(test == search)
        {

            if(check == repeat)
                return count;

          check++;
        }

        count++;
    }

}

int main()
{
    char sc[] = "cn:Y,x509UniqueIdentifier:Y,pseudonym:Y,name:Y,l:Y,street:Y,state:Y,postalAddress:Y,postalCode:Y,telephoneNumber:Y,emailAddress:Y";
    char testchar;  

    printf("Enter the search character: ");
    testchar = getc(stdin);

    printf("The search char found at: %d position.\n",findIndex(sc,testchar));

    fflush(stdin);

    while(testchar != 'N')
    {
        printf("The search char found at: %d posotion.\n",findIndex(sc,testchar));
        printf("Enter the search character: ");
        scanf("%c",&testchar);
                fflush(stdin);
    }        

    return 0;
}

The expected output was the index of character only one time, but I am getting this:-

[amarjeet@amarjeet ~]$ ./a.out 
Enter the search character: Y
The search char found at: 66 position.
The search char found at: 128 position.
Enter the search character: The search char found at: 0 position.
Enter the search character:

Where did I go wrong? Please let me know what is the issue and how to solve it.

Have you tried compiling with warnings enable (e.g., -Wall)? I suspect you would see a warning about function return value. — RTLinuxSW, Jun 07 '15 at 20:37
You'll also get a warning about comparing a `char` with a pointer, specifically "different levels of indirection". — Weather Vane, Jun 07 '15 at 20:50
I debugged your source code.Its also taking the newline character(as you are pressing enter) so its printing 2 times. — aakansha, Jun 07 '15 at 21:08

Eugeniu Rosca · Answer 1 · 2015-06-07T21:24:19.820

You probably want the main function to look like this:

int main()
{
    char sc[] = "cn:Y,x509UniqueIdentifier:Y,pseudonym:Y,name:Y,l:Y,street:Y,state:Y,postalAddress:Y,postalCode:Y,telephoneNumber:Y,emailAddress:Y";
    char testchar;

    printf("Enter the search character: ");
    scanf("%c",&testchar);
    while(testchar != '\n' && getchar() != '\n'); # discard any next chars

    while(testchar != 'N') {
        printf("The search char found at: %d position.\n",findIndex(sc,testchar));
        printf("Enter the search character: ");
        scanf("%c",&testchar);
        while(testchar != '\n' && getchar() != '\n'); # discard any next chars
    }
    return 0;
}

The above example produces the result:

$ > ./a.out
Enter the search character: Y
The search char found at: 66 position.
Enter the search character: .
The search char found at: 0 position.
Enter the search character: ,
The search char found at: 83 position.
Enter the search character: g
The search char found at: 0 position.
Enter the search character: N
$ >

PS: fflush() is not defined by ISO for input streams. It is defined in Microsoft's C runtime library, but is not portable.

score 1 · Accepted Answer · edited May 23 '17 at 11:58

You have one warning in your code which must be corrected

while((test = array[count]) != NULL)

The above line generates warning: comparison between pointer and integer.Therefore should be corrected as

while((test = array[count])!='\0')

In your output you are getting the index of character twice because newline character is also taken and its position is also getting printed(As you are pressing enter).

To avoid this you can do this

while(testchar != 'N')
{
       if(testchar!='\n'){//checking whether character is newline
        printf("The search char %d found at: %d posotion.\n",testchar,findIndex(sc,testchar));
        printf("Enter the search character: ");
        scanf("%c",&testchar);

        }
        else
        {
             scanf("%c",&testchar);//reading the newline character but not performing any operation(printing the index )
        }

}

Thats it your program works now.

Note:Use of fflush(stdin)is considered a bad practice and has undefined behaviour.Its better not to use it for flushing input streams as its unportable.See this more information Do not use fflush(stdin)

Output

Enter the search character: Y
The search char found at: 66 position.
The search char 89 found at: 128 position.
Enter the search character: J
The search char 74 found at: 0 position.
Enter the search character: o
The search char 111 found at: 85 position.
Enter the search character: N

Hope it helps.Happy Coding!!

Unexpected output from function

2 Answers2