i'm getting segmentation fault while using malloc with string pointers

Question

when i'm tryin' to use malloc with string pointers to scan, it's givin' a segmentation fault

main(){
    char *a;
    a = (char)malloc(50);
    printf("enter a string\t");
    scanf("%s", a);
    printf("%s\n", a);
}

Answer 1

a = (char)malloc(50);

Here, you meant to cast its type to char * instead of char.

Note that it's better not to cast the return type of malloc. See Do I cast the result of malloc?

Answer 2

Your main problem, apart from your using scanf is that you're casting a pointer (which is size 4 or 8 on 32 or 64 bit systems respectively) to a char, which is guaranteed to be size 1 as per standard.
Do not ignore compiler warnings. You should've seen something along the lines of:

warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
  a = (char) malloc(10);

warning: assignment makes pointer from integer without a cast [enabled by default]
  a = (char) malloc(50);

Casting a pointer type to char, only to assign it to a pointer variable makes no sense. If you want to make it absolutely clear that you are allocating enough memory to accomodate N chars, then you could write:

a = malloc(50 * sizeof(char));
//or better still
a = malloc(50 *sizeof *a);//50 times the size of whatever type a is pointing to...

But a char is always size 1, like I said before. Anyway: I set about fixing the code you posted:

The following copy-pasted code works just fine, provided you don't enter more than 49 chars:

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

int main( void )
{
    char *a = malloc(50);
    if (a == NULL) return EXIT_FAILURE;//<-- no memory available
    printf("enter a string\t");
    scanf("%s", a);
    printf("%s\n", a);
    free(a);//<== be tidy, free your memory, though here, it's a bit redundant
    return 0;
}

But really, look into alternatives to scanf, and never cast the pointer returned by malloc in C. C++ is a different matter.
Also, check for NULL pointers, to be safe.

Lastly: Don't ignore compiler warnings.

copy-paste & test here

you can provide stdin input at the bottom right hand side of the page, it'll print the string you provided