Segmentation Fault, array of pointers

Question

Why do I get the Segmentation Fault error? I've documented a lot but couldn't clarify this.

char * sir=malloc(50*sizeof(char));
char * aux;
int i;

for(i=1;;i++)
{
    fgets(aux, 50, stdin);

    if(strcmp(aux,"END")==0)
        break;
    else
    {
        sir[i]=malloc(50 * sizeof(char));
        strcpy(aux,sir[i]);
    }
}

If I use static allocation, then I get an infinite loop.

Answer 1

Pointer aux was not initialized and has indeterminate value

char * aux;

Thus in this loop the attempt to write data using the pointer

for(i=1;;i++)
{
fgets(aux, 50, stdin);
//...

results in undefined behaviour of the program.

Maybe it is a typo and you meant str instead of aux Nevertheless in any case this statement

sir[i]=malloc(50 * sizeof(char));

does not make sense.

Also this cpmparison is wrong

if(strcmp(aux,"END") == 0)

because the string read by using fgets can contain a new line character.