scanning values using pointers by passing memory address

Question

I am a student just started to learn programming using C. I am now learning pointers and I am trying to scan the value in function using pointers.But I keep getting error. I do not know why.Thanks for your answers.

void inputValue(int *numptr);
int main()
{
    int input;
    inputValue(&input);
    printf("%d\n", input);
    return 0;
}
void inputValue(int *inputptr)
{
    printf("Enter the value");
    scanf_s("%d", *inputptr);
}

Answer 1

I have solution for you, your function is wrong. Function scanf() needs address of variable not value of variable.

Your code:

void inputValue(int *numptr);
int main()
{
    int input;
    inputValue(&input);
    printf("%d\n", input);
    return 0;
}
void inputValue(int *inputptr)
{
    printf("Enter the value");
    scanf_s("%d", *inputptr); // this is the problem
}

You have to pass into scanf() address of variable.

So, your function should be:

void inputValue(int * inputPtr)
{
    printf("ENTER:");
    scanf("%d", inputPtr);
}

If you have integer variable and you want to read to it:

int n;
scanf("%d", &n); //you have to pass address of n

But if you have pointer to variable:

int n;
int * ptr = &n;
scanf("%d", ptr); //address of n -> it is pointing to n

But if you write *ptr it means value of variable it's pointing to:

int n;
int * ptr = &n;
scanf("%d", *ptr); //value of n - wrong

It is not passing address of variable but its value. So this is same:

int n;
scanf("%d", n); //value of n - wrong

Simple explanation pointers:

int n;
int * ptr = &n;

&n -> address of n
n -> value of n
ptr -> address of n 
*ptr -> value of n
&ptr -> address of pointer

And when we have function working with pointers:

void setval(int*, int);

void main(void)
{
     int n=54;
     setval(&n, 5); // passing address of n
     // now n=5
}

void setval(int * mem, int val)
{
     * mem = val; // it sets value at address mem to val
     // so it sets value of n to 5
     // if we passed only n not &n
     // it would mean address of value in n - if n would be 5 it's like we 
     // passed address in memory at 0x5
}