C quiz questions

[sovan chatt]

I need help with the following questions in
1)

int z,x=5,y=-10,a=4,b=2; 
z = x++ - --y * b / a;	

output?
2)

int a=10,b;
b=a++ + ++a;
printf("%d,%d,%d,%d",b,a++,a,++a);

I felt the answer would be 21,13,13,13 but the answer is 22,13,13,13.How b is coming as 22?
3)

void myFunc (int x) 
{ 
   if (x > 0)
   myFunc(--x); 
   printf("%d, ", x); 
} 

int main() 
{ 
   myFunc(5); 
   return 0; 
}  

I felt the answer should be 0, 1, 2, 3, 4, but is 0,0,1,2,3,4.How is the extra 0 coming?
4) why does 11 ^ 5 show 14
5)

 int a=5;
       a*=2+3

here a should have been 13(5*2+3) but it is coming as 25.How?
6)

#include <stdio.h> 
int i; 
void increment( int i ) 
{ 
   i++; 
} 

int main() 
{ 
   for( i = 0; i < 10; increment( i ) ) 
   { 
   } 
   printf("i=%d\n", i); 
   return 0; 
}  

Why is this creating an infinite loop?

[Mary Chellapa]

1. output = 10

[Mary Chellapa]

wow i could answer only first ... and i thought i was good in C.

[Stephan van Hulst]

Note that most of the answers are actually undefined, because C doesn't have proper rules for order of evaluation.

That said, here are some explanations using left-to-right evaluation.

1.)
z = x++ - --y * b / a;
z = 5++ - --(-10) * 2 / 4;
z = 5 - (-11) * 2 / 4;
z = 5 - (-22) / 4;
z = 5 - (-5);
z = 10;

2.)
b = a++ + ++a;
b = 10 + 12; // a = 12;
b = 22;

printf("%d,%d,%d,%d", b, a++, a, ++a);
printf("%d,%d,%d,%d", 22, 12, 13, 14);

3.)
myFunc(5) -> myFunc(4); printf("%d, ", 4);
myFunc(4) -> myFunc(3); printf("%d, ", 3);
myFunc(3) -> myFunc(2); printf("%d, ", 2);
myFunc(2) -> myFunc(1); printf("%d, ", 1);
myFunc(1) -> myFunc(0); printf("%d, ", 0);
myFunc(0) -> printf("%d, ", 0);

4.)
^ is the binary XOR operator. The calculation goes like this:

00001011 // 11
00000101 // 5
________
00001110 // 11 xor 5 = 14

5.)
Assignment operators (including compound assignment, like *=) have lowest precedence. The calculation goes:

a *= 2+3;
a *= 5;
a = 5*5;
a = 25;

6.)
You get an infinite loop because you're never incrementing the loop variable i. You're passing i to the increment function by value. The function increments a copy of i, and leaves the original variable like it was. A working increment function would look like this:

void increment(int* i) {
  (*i)++;
}

You would call it like this:

increment(&i);

[sovan chatt]

@Stephan van Hulst thanks for the explanations!.
I have got 1 more question.

scnaf("%2d%2d",&x,&y);

if I insert 358 and 453 what will x and y hold?

[Rob Spoor]

The correct answer to that is "try it yourself and find out".