output of following c code

Code:

---

#include<stdio.h>
void main()
{
int a;
printf("a contains %d\n");
}

---

this is giving some junk value where as

Code:

---

#include<stdio.h>
void main()
{
float a;
printf("a contains %f\n");
}

---

this is not giving any value.I am not getting why is it so and could you please tell me what is the concept behind it?

%d and %f tell printf() than an additional argument has been passed. Your code does not pass an additional argument, so exhibits undefined behaviour.

Your first example needs to be

Code:

---

#include<stdio.h>
int main()
{
int a;
printf("a contains %d\n", a);
}

---

Note the changes I have highlighted in red.

a still needs to be initialised though, before trying to print it.
int a = 42;

It's int main(void), not void main(). Let me guess...Turbo C?

And this should be in C Programming, not C++.

EDIT: Oops. grumpy already covered the int main issue.