uninitialized local variable 'num' used?

Question

#include<stdio.h>
#include<conio.h>

int main()
{
    int num;
    printf("Enter your number \n");
    scanf_s("%d", num);
    printf("Your number is %d", num);
    _getch();
    return 0;
}

When i build the above code in VS2013 it gives me following error :

error C4700: uninitialized local variable 'num' used ?? Whhat would be the reason for this ??

score 5 · Accepted Answer · answered Jan 31 '14 at 14:01

5

You forgot the &:

scanf_s("%d", &num);

scanf expect a pointer, so it was reading the value of num to find the address to write the user input (and num was not initialized, that's why the compiler raise a warning). But what you really meant is the address of num itself.

answered Jan 31 '14 at 14:01

fede1024

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23

btw what is `_s`? I don't know.. – Grijesh Chauhan Jan 31 '14 at 14:02
1

Is the "secure" version of scanf, that can prevent buffer overflows. – fede1024 Jan 31 '14 at 14:03
I also dont know "scanf_s" i wrote "scanf" the intellisense suggested me to make it scanf_s otherwise it was giving and error. – TheSpy Jan 31 '14 at 14:07
okay fede thats great :) – TheSpy Jan 31 '14 at 14:07
Interesting OP is using a "secure" version of `scanf()` on an uninitialized variable yet does not check the return value. – chux - Reinstate Monica Jan 31 '14 at 14:07
1

@chux OP is using secure version in insecure way :P – Grijesh Chauhan Jan 31 '14 at 14:09
@SaadAhmed For a short explanation about scanf_s look here http://stackoverflow.com/a/9986940/1025899 – fede1024 Jan 31 '14 at 14:09

uninitialized local variable 'num' used?

1 Answers1