## INDEX

### Looping questions in c and answers

Looping questions and answers with explanation for written test exam and interview in c programming language

(1)

What will be output of following c code?

#include<stdio.h>
extern int x;
int main(){
do{
do{
printf("%o",x);
}
while(!-2);
}
while(0);
return 0;
}
int x=8;

## Explanation

Output: 10
Explanation:
Here variable x is extern type. So it will search the definition of variable x. which is present at the end of the code. So value of variable x =8
There are two do-while loops in the above code.  AS we know do-while executes at least one time even that condition is false.  So program control will reach  at printf statement at it will print octal number 10 which is equal to decimal number 8.
Note: %o is used to print the number in octal format.
In inner do- while loop while condition is ! -2 = 0
In C zero means false.  Hence program control will come out of the inner do-while loop.   In outer do-while loop while condition is 0. That is again false. So program control will also come out of the outer do-while loop.

### Hide

(2)
What will be output of following c code?

#include<stdio.h>
int main(){
int i=2,j=2;
while(i+1?--i:j++)
printf("%d",i);
return 0;
}

## Explanation

Output: 1
Explanation:
Consider the while loop condition: i + 1 ? -- i : ++j
In first iteration:
i + 1 = 3 (True)
So ternary operator will return -–i i.e. 1
In c 1 means true so while condition is true. Hence printf statement will print 1
In second iteration:
i+ 1 = 2 (True)
So ternary operator will return -–i i.e. 0
In c zero means false so while condition is false. Hence program control will come out of the while loop.

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(3)
What will be output of following c code?

#include<stdio.h>
int main(){
int x=011,i;
for(i=0;i<x;i+=3){
printf("Start ");
continue;
printf("End");
}
return 0;
}

## Explanation

Output: Start Start Start
Explantion:
011 is octal number. Its equivalent decimal value is 9.
So, x = 9
First iteration:
i = 0
i < x i.e. 0 < 9  i.e. if loop condition is true.
Hence printf statement will print: Start
Due to continue keyword program control will come at the beginning of the for loop and value of variable i will be:
i += 3
i = i + 3 = 3
Second iteration:
i = 3
i < x i.e. 3 < 9 i.e. if loop condition is true.
Hence printf statement will print: Start
Due to continue keyword program control will come at the beginning of the for loop and value of variable i will be:
i += 3
i = i + 3 = 6
Third iteration:
i = 3
i < x i.e. 6 < 9 i.e. if loop condition is true.
Hence printf statement will print: Start
Due to continue keyword program control will come at the beginning of the for loop and value of variable i will be:
i += 3
i = i + 3 = 9
fourth iteration:
i = 6
i < x i.e. 9 < 9 i.e. if loop condition is false.
Hence program control will come out of the for loop.

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(4)What will be output of following c code?

#include<stdio.h>
int main(){
int i,j;
i=j=2,3;
while(--i&&j++)
printf("%d %d",i,j);
return 0;
}

## Explanation

Output: 13
Explanation:
Initial value of variable
i = 2
j = 2
Consider the while condition : --i && j++
In first iteration:
--i && j++
= 1 && 2 //In c any non-zero number represents true.
= 1 (True)
So while loop condition is true. Hence printf function will print value of i = 1 and j = 3 (Due to post increment operator)
In second iteration:
--i && j++
= 0 && 3  //In c zero represents false
= 0  //False
So while loop condition is false. Hence program control will come out of the for loop.

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(5)What will be output of following c code?

#include<stdio.h>
int main(){
static int i;
for(++i;++i;++i) {
printf("%d ",i);
if(i==4) break;
}
return 0;
}

## Explanation

Output: 24
Explanation:
Default value of static int variable in c is zero. So, initial value of variable i = 0
First iteration:
For loop starts value: ++i i.e. i = 0 + 1 = 1
For loop condition: ++i i.e. i = 1 + 1 = 2 i.e. loop condition is true. Hence printf statement will print 2
Loop incrimination: ++I i.e. i = 2 + 1 =3
Second iteration:
For loop condition: ++i i.e. i = 3 + 1 = 4 i.e. loop condition is true. Hence printf statement will print 4.
Since is equal to for so if condition is also true. But due to break keyword program control will come out of the for loop.

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(6)What will be output of following c code?

#include<stdio.h>
int main(){
int i=1;
for(i=0;i=-1;i=1) {
printf("%d ",i);
if(i!=1) break;
}
return 0;
}

## Explanation

Output: -1
Explanation:
Initial value of variable i is 1.
First iteration:
For loop initial value: i = 0
For loop condition: i = -1 . Since -1 is non- zero number. So loop condition true. Hence printf function will print value of variable i i.e. -1
Since variable i is not equal to 1. So, if condition is true. Due to break keyword program control will come out of the for loop.

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(7)What will be output of following c code?

#include<stdio.h>
int main(){
for(;;) {
printf("%d ",10);
}
return 0;
}

## Explanation

Output: Infinite loop
Explanation:
In for loop each part is optional.

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(8)What will be output of following c code?

#include<stdio.h>
int r();
int main(){
for(r();r();r()) {
printf("%d ",r());
}
return 0;
}
int r(){
int static num=7;
return num--;
}

## Explanation

Output: 5 2
Explanation:
First iteration:
Loop initial value: r() = 7
Loop condition: r() = 6
Since condition is true so printf function will print r() i.e. 5
Loop incrimination: r() = 4
Second iteration:
Loop condition: r() = 3
Since condition is true so printf function will print r() i.e. 2
Loop incrimination: r() = 1
Third iteration:
Loop condition: r() = 0
Since condition is false so program control will come out of the for loop.

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(9)What will be output of following c code?

#include<stdio.h>
#define p(a,b) a##b
#define call(x) #x
int main(){
do{
int i=15,j=3;
printf("%d",p(i-+,+j));
}
while(*(call(625)+3));
return 0;
}

## Explanation

Output: 11
Explanation:
First iteration:
p(i-+,+j)
=i-++j   // a##b
=i - ++j
=15 – 4
= 11
While condition is : *(call(625)+ 3)
= *(“625” + 3)
Note: # preprocessor operator convert the operand into the string.
=*(It will return the memory address of character ‘\0’)
= ‘\0’
= 0  //ASCII value of character null character
Since loop condition is false so program control will come out of the for loop.

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(10)

#include<stdio.h>
int main(){
int i;
for(i=0;i<=5;i++);
printf("%d",i)
return 0;
}

## Explanation

Output: 6
Explanation:
It possible for loop without any body.

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(11)What will be output of following c code?

#include<stdio.h>
int i=40;
extern int i;
int main(){
do{
printf("%d",i++);
}
while(5,4,3,2,1,0);
return 0;
}

## Explanation

Output: 40
Explanation:
Initial value of variable i is 40
First iteration:
printf function will print i++ i.e. 40
do - while condition is : (5,4,3,2,1,0)
Here comma is behaving as operator and it will return 0. So while condition is false hence program control will come out of the for loop.

### Hide

(12)What will be output of following c code?

#include<stdio.h>
char _x_(int,...);
int main(){
char (*p)(int,...)=&_x_;
for(;(*p)(0,1,2,3,4); )
printf("%d",!+2);
return 0;
}
char _x_(int a,...){
static i=-1;
return i+++a;
}

## Explanation

Output: 0
Explanation:
In c three continuous dot represents variable number of arguments.
p is the pointer to the function _x_
First iteration of for loop:
Initial value: Nothing // In c it is optional
Loop condition: (*p)(0,1,2,3,4)
= *(&_x_)(0,1,2,3,4)  // p = &_x_
= _x_(0,1,2,3,4)    //* and & always cancel to each other
= return i+++a
= return i+ ++a
= return -1 + 1
= 0
Since condition is false. But printf function will print 0. It is bug of c language.

### Hide

(13)What will be output of following c code?

#include<stdio.h>
int main(){
int i;
for(i=10;i<=15;i++){
while(i){
do{
printf("%d ",1);
if(i>>1)
continue;
}while(0);
break;
}
}
return 0;
}

## Explanation

Output: 1 1 1 1 1 1
For loop will execute six times.
Note: continue keyword in do-while loop bring the program its while condition (while(0)) which is always false.

### Hide

(14)How many times this loop will execute?

#include<stdio.h>
int main(){
char c=125;
do
printf("%d ",c);
while(c++);
return 0;
}

## Explanation

Output: Finite times
Explanation:
If we will increment the char variable c it will increment as:
126,127,-128,-127,126 . . . .   , 3, 2, 1, 0
When variable c = 0 then loop will terminate.

### Hide

(15)What will be output of following c code?

#include<stdio.h>
int main(){
int x=123;
int i={
printf("c" "++")
};
for(x=0;x<=i;x++){
printf("%x ",x);
}
return 0;
}

## Explanation

Output: c++0 1 2 3
Explanation:
First printf function will print: c++ and return 3 to variable i.
For loop will execute three time and printf function will print 0, 1, 2 respectively.

### Hide

Looping tutorial in c

Sankalp said...

very good examples and explanations are very clear.
excellent efforts :)

GUPTA said...

Hey I really apprecicate ur site....Awesome explanations....This is the first page i hv read and really understood....Kudos to u guys !!
:)

blogger.MalapaTi said...

hey i have one doubt in Q:15
have a Great Day!!

Ravi said...

Yes this all are very important question, and also explanation is very clear and in very nice manner.

Thanx A Lot !!!!

Unknown said...

In question 9

can you explain macro a##b

Unknown said...

very useful page

swarup said...

can u please explain how the return stmt returns 3 value to i variable in 15th question

Priyanka kumari said...

Return type of prinf function is integer which is total numbers of characters its prints. In this example printf("c" "++") it printing three characters 'c','+' and '+' so it will return 3.

Priyanka kumari said...

in printf statement
%x : prints number in hexadecimal format
%i : prints number in integer format
%d : prints number in decimal format

Priyanka kumari said...

## is oken pasting operator.Better go through this link:
Use of # and ## operator in c programming language

Anonymous said...

hi ritesh u r doing great job..

this is helping to lot of guys like us

DHANU said...

GOOD JOB

Anonymous said...

wt is looping

Roja said...

can you explain macro a##b and #x

Ahmed Ismail said...

First: Really it is a great page and it benefit me alot to fresh my memory.
For Q.12:
There is not any bug.
but the compiler evaluated i+++a as following: i++ + a.
So, we have (-1)++ + 0 = -1 .... true and printf() statement is executed.

i+++a is evaluated as i++ + a.

That is due to compiler really do not ignore all white spaces.

for the case: i+++a: it handle the variable i then it looks for the longest possible operator.
we have 2 options: + , ++ / it cannot consider +++ as an operator as there is not an operator (+++)
The longest one is ++.
then the remained operator is +. and then handle the next variable.

To make idea clear:
consider we have:
i = -1;
a =0;
z = i+++++a;

Now the compiler will parse it: i++ ++ + a. and it will bring a compilation error. (Lvalue required as increment operand).

If we modified the expression and added some white space it will work.
z = i++ + ++a;
it works and result will be zero.

Unknown said...

c is very imprtnt sub

enorÐ¼ous Ð½aÐ²iÐ² said...

At one college, the tuition for a full-time student is \$6,000 per semester. It has been announced that the tuition will increase by 2% each year for the next 5 years. Design a program with a loop that displays the projected semesters tuition amount for the next five years.
how would this be done?

Anonymous said...

#include
int main()
{
int semf=6000,prof;//semester fees , projected fees
int i,y=0;

for(i=1;i<=10;i++)
{
semf=(semf+6000*2/100);
prof=semf;
printf(" Tution amount for %d semester %d\n",y=y+1,prof);

}

getch();
return 0;
}

hafeehathim said...

Hi,
can any one explain how does the following while loop work?
while(5,4,3,2,1,0)

varsha said...

can any 1 give me solution for 1+1/3+1/5+....+1/n
plzzzzzzz guys

vykunta@galavili.com said...

ritesh kumar good hard work..

Anonymous said...

printf("%d",!+2); pls explain it and what is comma(,) operator in c and how it works in while loop

Anonymous said...

Is it possible to create a
C program to find the largest and smallest of n numbes inputed by user using while loop?

SOYAM KANNARAJU said...

the way of explanation and way of writing is so ............great..............

Unknown said...

what will be output of following prograam??

for (m=0; m<3; ++m)
t=(m%2)? m:m+2;
printf("%d",t)

anjaneyareddy said...

tanx frnds
and Excellent

Ankit ghiya said...

what is the difference of using %d and %i?
I think both produce same result.

Gopal Singh said...

output will be 2

Unknown said...

Unknown said...

Question 9:
Could somebody please explain to me how *("625" + 3) return the memory address of character '\0'?
what is this expression mean ("625" + 3) in C?

Unknown said...

Here loop will never execute because the last number is 0.
Suppose if you try this "while(5,4,3,2,1)" the loop will never end because the last number is one.
It means while takes the last number as condition.

Unknown said...

#include

int main()
{
int i,great=0,low=0,a[8];
printf("Enter 8 numbers: ");
for(i=0;i<8;i++)
{
scanf("%d ",&a[i]);
}
great=a[0];
low=a[0];
while(i--)
{
if(greata[i])
{
low=a[i];
}
}
printf("Greatest: %d \n",great);
printf("Lowest : %d \n",low);
return 0;
}

Unknown said...

Here you have to know the operators Associativity. Both '+' & '!' have same priority. The Associativity is from right to left. So first addition will take place. 0+2 is 2. And "!2=0". Any positive number with NOT symbol is equal to zero.

Srujan said...

Agree with this explanation.

Unknown said...

write a c program to generate the customer bill for a point of sale system used in a retail shop. The program must use a predefined list of ANY 5 items, while the user will enter the item code and the quantity for n number of items selected by the customer, to print the the bill including a goods and service tax of 6%. ( I am stuck here creating the predefined list and giving item codes. Can any of you experts can help me out as soon as possible? )

Unknown said...

Is there any1 here who could help me?

Unknown said...

what is the meaning of !-2

Unknown said...

i love you

priyank said...

Can You Improve the Explanation Section..
I didn't find your explanation Too concise and clear

Unknown said...

#include
int main()
{
int semsterfee=6000,projectfee;
int i,y=1;
printf("Tution amount for 1 semester = \$6000\n");

for(i=2;i<=10;i++)
{
semsterfee=(semsterfee+6000*2/100);
projectfee=semsterfee;
printf(" Tution amount for %d semester= \$%d\n",y=y+1,projectfee);

}

getch();
return 0;
}

Unknown said...

#include
int main()
{
int m,t;
for (m=0; m<3; ++m)
t=(m%2)? m:m+2; // Output is 4
{
printf("output=%d",t);
}

}

Unknown said...

%i : prints number in integer format
%d : prints number in decimal format

Unknown said...

i=Not oprater,its revers the value

Unknown said...
This comment has been removed by the author.
Unknown said...

These are so tricky and so helpful in understanding the concepts! Thank you!

Shaem said...

Pls help me...
when i write a code like this...

#include
int main(void)
{
int count=0;
while (count < 10 && ++count)
printf("count is %d\n", count);
return 0;
}
output :
1 2 3 4 5 6 7 8 9 10
But when i change ++ count by count ++
#include
int main(void)
{
int count=0;
while (count < 10 && count++)
printf("count is %d\n", count);
return 0;
}
output : Nothing.
Pls give me a solution.

Good questions

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KITS Technologies said...
Anonymous said...

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