CODEWITHSUNDEEP
c
Afshin Ahmadi
Afshin Ahmadi

Reputation: 37

Passing a variable into a function and changing its global value

I am trying to pass a variable into a function and change its global value but it does not work. Here is the simplified code:

int main()
{
   int *Num = malloc (sizeof (int));
   ChangeValue(&Num);
   printf("Number is %i\n", Num);
}


int ChangeValue(int *temp)
{
   *temp = 10
}

The error message is: 

        expected 'int *' but argument is of type 'int **'

I tried to change the function to int ChangeValue(int **temp) but received the following error:

        warning: assignment makes pointer from integer without a cast.

Any suggestions?

Upvotes: 0

Views: 57

Answers (2)

Tommalla
Tommalla

Reputation: 317

Variable Num is a pointer to an int (int*). Function ChangeValue(int*) takes a pointer to an int (int*). However, you are passing a pointer to Num (int**) to it.

Short answer: remove & before Num in ChangeValue(&Num);

Long answer: You seem to have a problem understanding how pointers work, you might want to read more about this before going further.

Upvotes: 2

Schwern
Schwern

Reputation: 164799

int *Num means Num is of type int *. Since it's already an integer pointer, there's no need to take its address again when you pass it to your function that takes an int *.

ChangeValue(Num);

OTOH, since it is a pointer you will have to dereference it to use it as an integer, like with printf.

printf("Number is %i\n", *Num);

Upvotes: 3

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