Thread: C help

When you find yourself copy/pasting blocks of code, then that code is a good candidate for a function. The only challenge you may face, if you're still very new, is how to get two values (e.g. "first" and "second") from a function, when a function can only return one value. The solution is to pass pointers to the variables of interest, so their values can be updated in the called function.

For example:

Code:

#include <stdio.h>

void get_two_numbers( int *n1, int *n2 );  // expects two pointers to int

int main(void)
{
    int x1, x2;

    get_two_numbers(&x1, &x2);  // pass addresses of x1 and x2

    printf("\nx1 is %d\nx2 is %d\n", x1, x2);

    return 0;
}

void get_two_numbers( int *n1, int *n2 )
{
    int num1, num2;

    puts("Enter 1st number:");
    scanf("%d", &num1);         // error checking omitted
    puts("Enter 2nd number:");
    scanf("%d", &num2);         // error checking omitted

    *n1 = num1;  // dereference "n1" and store the value of "num1"
    *n2 = num2;  // dereference "n2" and store the value of "num2"
}

In "get_two_numbers()", you wouldn't even need local variables. Note the slightly difference scanf() calls, since "n1" and "n2" are already pointers:

Code:

void get_two_numbers( int *n1, int *n2 )
{
    puts("Enter 1st number:");
    scanf("%d", n1);         // error checking omitted; no '&' operator since n1 already a pointer
    puts("Enter 2nd number:");
    scanf("%d", n2);         // error checking omitted; no '&' operator since n2 already a pointer
}

If this seems over your head at this time, an easier solution would be to pass a char that indicates the operation you wish to perform. Then your function can read two values, perform the indicated operation, and simply return an answer.

Matticus thank you very much for help, you are very good in teaching. Next chapter i think is about pointers and im gonna read it today and try this solution that you told me.

If i get it right, in function get_two_numbers() i dont need num1 and num2 because there are pointers n1 and n2 and i dont need to use & for pointers in scanf, same as string for example

Code:

("%s", string)

.

Originally Posted by kzzmzz

If i get it right, in function get_two_numbers() i dont need num1 and num2 because there are pointers n1 and n2 and i dont need to use & for pointers in scanf, same as string for example

Code:

("%s", string)

.

Assuming you mean scanf("%s", string), then you are correct. In this example, "string" is (presumably) a char array, so using the name of the array by itself acts as a pointer to its first element - since it's a pointer already, you don't need the '&' operator. In the example I posted, "n1" and "n2" are already pointers, so you don't need the '&' there either.

Sounds like you understand what's going on. Keep up the good work.

Yes i mean scanf("%s", string). Thank you very much again, can i send you pm or ask you here on forum if i got in trouble again?

You're welcome. Just create a new thread if you have any problems going forward, you'll get the benefit of various members' advice.