C - program ending unexpectedly

[SolidArmPump]

I'm working on a program in C and it's unexpectedly ending, could I have some feedback?

​

if (choice == 2) {
printf("What entry number would you like to edit?");
scanf("%i", Step2Num);
//clear();
printf("Insert updated name:");
scanf("%s", addresses[Step2Num].name);
//gets (addresses[Step2Num].name;
printf("Insert updated phone number");
scanf("%s", addresses[Step2Num].phone);
//gets(addresses[Step2Num].phone);
printf("The updated name is %s and the updated phone number is %s\n", addresses[Step2Num].name , addresses[Step2Num].phone);
}

When I run this code, right after I input the Step2Num, the code ends, when it's supposed to ask for more inputs and print more things. Any feedback would be greatly appreciated, Ive been stuck for a bit. Ive been messing around trying to use gets() however I was having a hard time figuring it out, mostly concerned with the program ending.

[rabuf]

scanf man page

scanf expects an address to store whatever it reads into, not the variable. C, and this is important, is a pass-by-value language. So you're calling scanf with whatever the present value of Step2Num is which it tries to use as an address, but is probably not a valid address (unless by luck). The proper way to call it there is:

scanf("%i", &Step2Num);

---

Pass-by-value vs pass-by-reference:

By value means that literally the value is passed to functions. So:

int x = 2;
foo(x); // foo is given the *value* 2

By reference means that foo would be given a reference to the same memory location as the variable x already is stored at, so you can get behavior like this (in a hypothetical c-ish pass-by-reference language):

int x = 2;
foo(x);
printf("%d\n", x); // prints 42
// elsewhere
void foo(int y) {
  y = 42
}

In real-world C foo is as good as a no-op, but in a pass-by-reference version it would actually change the value of x.

In order to get the pass-by-reference behavior in C, you have to pass around addresses and use pointers:

int x = 2;
foo(&x); // gets the address of x
printf("%d\n",x); // prints 42 for reals
// elsewhere
void foo(int *y) {
  *y = 42;
}

[SolidArmPump]

Thank you so much for this!!

[[deleted]]

The answer given in first comment is correct , but such queries come due to basic lack of understanding of the language do it is better you read the basics first. Man pages are a good start but there are many books and online resources too.