Question

int *fun (int *x)f int value *xtt return &value; int main) int pl; int **p2; int a; char str [5] printf ("Enter a number:") scanf("%d", a) ; printf ("Enter a line:") gets (str); p1-malloc(sizeof (int)) *pl-p2; p2-malloc(sizeof (int)); pl-fun (a); n-0; for (pl-stripl<-str+5;pl++) if (isdigit (pl)) at+; return 0;

please help me with this question

(in C programming language and Unix)
computer system book 3 edition

Answer 1

Error in:
scanf("%d", a);
with scanf, you need to pass the address of variable, not the variable itself.. So this may cause crash in program. The correct code will be:
scanf("%d", &a);

Error: gets(str);
This does not give a compile time error, but may result in a runtime error. The gets function, keeps on reading the line from console, until a new line is found. Now str has just memory for 5 characters, so if used enters string of more than 5 characters, then program may crash. The correct code will be:
fgets(str, 4, stdin);  // leaving one character for '\0'

Error: *p1 = p2;
p1 is a pointer to int, while p2 is a pointer to pointer to int. So p2 is basically an address, which should not be kept in integer variable.
Correct code: *p1 = **p2;

Error: p2 = malloc(sizeof(int));
p2 is a pointer to pointer to int, while it allocates memory for only an integer.. which is 
wrong.
Correct code: p2 = malloc(sizeof(int *));

Error: p1 = fun(a);
You are getting some other integer's address from outside, but the int which got allocated in main function, that reference will get miss after this statement.. hence before executing this statement, we should free memory pointed by p1.
Correct: free(p1); p1 = fun(a);

Error: for loop
We are using a integer pointer to traverse the character array which is wrong.. 
Correct Code: Use a character pointer.