Thread: Scanf/gets string act as sort of a stack .

Hello everyone ,

I have a function in my code which gets a string , sends it to another function for validation , and if the string
turns out to be invalid , then it calls the function again (which gets the string) .

I have made a simple code which demonstrates my question :

Code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char string[30];
    short i;
    scanf("%s",string);
    if(strcmp(string,"1")==0)
        main();
    printf("%s",string);
}

Let us say that a valid string is all the strings which are not "1" .
If one enters three times "1" ("1", calls main() , "1" ,etc..) and then enters "2" , the output would be : "2111" .

My first thought was that the string wont re-initialize , so I have added a bit to my code which would put '\0' (end of string)
in each char :

Code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char string[30];
    short i;
    for(i=0;i<30;i++)
        string[i]='\0';
    scanf("%s",string);
    if(strcmp(string,"1")==0)
        main();
    printf("%s",string);
}

As you can see - right after the declaration of the variable , I loop through each char and put '\0' in it ,
but the output stays the same ("2111") .
I have tried to replace the input/output functions , replace the manual loop to strcpy(string,"") , the output stays the same .

I`d really like to know what am I missing here , why wont the output just be "2" ?

Thank you much ,

Danny .

scanf("%s",&string)

^ A string is already a pointer to the first char , there is no need to specify an ampersand there (also I tried it and the output is the same) .

Thank you for the quick answer though ,

Danny .

Originally Posted by Dann Shem

@stahta01 Thanks! In my code (this is just an example , it is not my code which I`m talking about) the recursive function is not main() .
I have updated the code to the following :

Code:

#include <stdio.h>
#include <stdlib.h>

void testOutput()
{
    char string[30];
    short i;
    for(i=0;i<30;i++)
        string[i]='\0';
    scanf("%s",string);
    if(strcmp(string,"1")==0)
        main();
    printf("%s",string);
    return;
}
int main()
{
    testOutput();
    return 0;
}

And the output stays the same .

Thanks again ,

Danny .

You are STILL calling main!!!!

Tim S.

True , sorry , edited .
Output is still the same .

Thanks ,

Danny .

I suggest trying the below code; it might work.

Code:

if(strcmp(string,"1")==0){
        testOutput();
} else {
    printf("%s",string);
}

You are creating new storage for string every time you enter your function.
Maybe you want to pass it? Or make it static?

My dear friends , thank you for everything , but this is not my actual code - this is an example which results the same as my code .
My actual code is validating an input for a name a user enters which will follow to enter to a linked list .
I sure can avoid this , but the question is just out of curiosity , the code is already fixed .

Thanks again to all of you ,

Danny .

Any luck ?

Thanks , Danny .

The code has been fixed indeed , but as I said - I`m still very curious for why the output is what it is .
What does a fixed code give me if I do not understand the root of the problem with the previous one ?

Maybe you can get us up to date by (re)posting the code and your specific question(s)?