Simple c program-please explain output.

[hitesh.incept]

int main()
{
     int a=7, t=0;
     t=--a+--a+a+++a;
     printf("%d",t);
}

output: 20

I could not understand why it prints '20' ? please explain it !

[DELOCH]

a=7
t=(--a)+(--a)+(a++)+a;
=6 + 6 + 0 + 8 = 20

a++ becomes 0 in that situation for some reason which I do not understand

[slickuser]

I believe the pre-decrement (or increment) will happen entirely before the final calculation. The post-increment (or decrement) will happen after the calculation. Thus:

a=7;
two decrements happen first and a=5 and the increment happens after the calculation;
so: 5 + 5 + 5 + 5 = 20.

The value of 'a' after the calculation is a=6.

If you instead did:
t=--a+--a+a+++a+++a;
the value of t=25 (5+5+5+5+5) and a=7.

[rileyvanzeeland]

You are essentially doing this-

int main()
{
         int a=7, t=0;
	 --a;
	 --a;
	 
         t=a;
	 t+=a;
	 t+=a;
	 t+=a;
	 
	 a++;
	 
         printf("%d",t);
}