C Programming - Expressions - Discussion

Hi friends.

In gcc compiler the statement use stack code of:

#include<stdio.h>
int main()
{
int a=35;
printf("%d %d %d %d %d ",a++,a++,++a,a++,++a);
return 0;
}

OUTPUT gcc: 39 38 40 36 40.

And only add to it a++ statement.

#include<stdio.h>
int main()
{
int a=35;
printf("%d %d %d %d %d %d",a++,a++,++a,a++,++a,a++);
return 0;
}

What is output?

Stack contain 36,37,38,39,40,41 when first %d print 40 because a++ post increment if ++a o/p is 41.

2nd %d o/p is 39 if a++ o/p 41.

All post increment represent it stack value and pre increment is higest value.

The o/p of above explained program is not 0030
Its 0130
Execution in that s 4m right to left
STEP1: FIRST the variable IS assigned as 35 at the time of declaration
STEP2: Then in the printf statement variable a is assigned as a=30(as execution is from right to left)
step 3: Then a<=50 becomes 30<=50 &the value of that relational expression is 1(30<=50 is true)
step 4: Then a==40 becomes 30==40&its value is zero
The execution is from right to left but the values are printed as per the seqence. So ans is 0130.

GCC or Turbo C compilers are implementations to compile C language. C language hasn't described everything, somethings are implementation dependent. Like the output Neetu has explained is right for GCC but not for Turbo C.

To be precise a compiler works on a CFG (Please refer to it from Wikipedia and leave it if you don't about Finite Automata and Grammar). Dennis Ritchie has explained it in his book "The C Programming Language".

Hi Friends...
The evalution order in c is:Right to left but in c++ is Left to Right.
During the display, the values are dispaly from left to right.(both c and c++)

#include<stdio.h>
int main()
{
int a=35;
printf("%d %d %d ",a==40,a<=50,a=30);
return 0;
}


O/P : 0 1 30


For eg::
main()
{
int i=5;
printf("%d %d",++i,++i);
}

O/P:: in c::7,6 but in c++ 6,7
But it varies depends on the compiler..

int j=5,s=5,i=0,m=5,n=5,q=0,h=5;
i=m++ + ++n-j-- - --s;
q=h++ + ++h - h-- - --h;
System.out.println("q:"+q);
System.out.println("i:"+i);
System.out.println("j:"+j);
System.out.println("s:"+s);
System.out.println("j:"+m);
System.out.println("s:"+n);

can you explain this one?

@Shefali : Difference between GCC and Turbo C compiler is that they are made by different companies.

But the standard for C language is same.

Then you must be asking why their is so much difference in output in two compilers.

So always consider GCC as prime because it is industrial standard C compiler. And Turbo C is old compiler which is not used anymore now except educational purpose to simplify complexity.

It is right.. for example:


#include<stdio.h>
int main()
{
int a=35;
printf("%d %d %d ",a==40,a<=50,a=30);
return 0;
}

will u see the out put in this .. the out put will be
0 0 30
because it can read right to left in print statement, when it we write the options continuously(a==40,a<=50,a=30).

Output will be 3 and 4 as in printf() function expression is evaluated from right to left. and displayed from left to right. As here ++i will be evaluated first then i becomes 3 and than ++j will be evaluated than j becomes 4.

But as output is left to right.

Hence output is 4 3 (gcc compiler).

i++ is postfix increment and ++i is prefix increment. As example:

void main()
{
int i=1;
i=i++;
printf("%d",i);
}

After execute it print output = 2.

In prefix increment:

main()
{
i=1;
i=++i;
}

After execute it print the output = 2.

Post and pre increments evaluated in left to right order.

And displayed left to right order;

Example: i = 2;.

++i, --i.

First we have to calculate --i after that ++i.

Those values are 1, 2.

Displayed values are 2, 1.