Red Hat Most Frequently Asked C Language Interview Questions Answers

Write a program to reverse a given number in C?

#include<stdio.h>
#include<conio.h>
main()
{
int n, reverse=0, rem;    //declaration of variables.
clrscr(); // It clears the screen.
printf("Enter a number: ");
scanf("%d", &n);
while(n!=0)
{
     rem=n%10;
     reverse=reverse*10+rem;
     n/=10;
}
printf("Reversed Number: %d",reverse);
getch();  // It reads a character from the keyword.
}

What does the && operator do in a program code?

The && is also referred to as AND operator. When using this operator, all conditions specified must be TRUE before the next action can be performed. If you have 10 conditions and all but 1 fails to evaluate as TRUE, the entire condition statement is already evaluated as FALSE.

In C programming, what command or code can be used to determine if a number of odd or even?

There is no single command or function in C that can check if a number is odd or even. However, this can be accomplished by dividing that number by 2, then checking the remainder. If the remainder is 0, then that number is even, otherwise, it is odd. You can write it in code as:

if (num % 2 == 0)

printf(&quot;EVEN&quot;);
else
printf(&quot;ODD&quot;);

What does the format %10.2 mean when included in a printf statement?

This format is used for two things: to set the number of spaces allotted for the output number and to set the number of decimal places. The number before the decimal point is for the allotted space, in this case it would allot 10 spaces for the output number. If the number of space occupied by the output number is less than 10, addition space characters will be inserted before the actual output number. The number after the decimal point sets the number of decimal places, in this case, it’s 2 decimal spaces.

What are logical errors and how does it differ from syntax errors?

Program that contains logical errors tend to pass the compilation process, but the resulting output may not be the expected one. This happens when a wrong formula was inserted into the code, or a wrong sequence of commands was performed. Syntax errors, on the other hand, deal with incorrect commands that are misspelled or not recognized by the compiler.

Red Hat Most Frequently Asked C Language Interview Questions Answers

What is the use of a semicolon (;) at the end of every program statement?

It has to do with the parsing process and compilation of the code. A semicolon acts as a delimiter, so that the compiler knows where each statement ends, and can proceed to divide the statement into smaller elements for syntax checking.

What is difference between i++ and ++i?

1) The expression ‘i++’ returns the old value and then increments i. The expression ++i increments the value and returns new value.
2) Precedence of postfix ++ is higher than that of prefix ++.
3) Associativity of postfix ++ is left to right and associativity of prefix ++ is right to left.
4) In C++, ++i can be used as l-value, but i++ cannot be. In C, they both cannot be used as l-value.

What is l-value?

l-value or location value refers to an expression that can be used on left side of assignment operator. For example in expression “a = 3”, a is l-value and 3 is r-value.
l-values are of two types:
“nonmodifiable l-value” represent a l-value that can not be modified. const variables are “nonmodifiable l-value”.
“modifiable l-value” represent a l-value that can be modified.

How to write your own sizeof operator?

#define my_sizeof(type) (char *)(&type+1)-(char*)(&type)

How will you print numbers from 1 to 100 without using loop?
We can use recursion for this purpose.

/* Prints numbers from 1 to n */
void printNos(unsigned int n)
{
  if(n > 0)
  {
    printNos(n-1);
    printf("%d ",  n);
  }
}

What is volatile keyword?

The volatile keyword is intended to prevent the compiler from applying any optimizations on objects that can change in ways that cannot be determined by the compiler.
Objects declared as volatile are omitted from optimization because their values can be changed by code outside the scope of current code at any time. See Understanding “volatile” qualifier in C for more details.

Can a variable be both const and volatile?

yes, the const means that the variable cannot be assigned a new value. The value can be changed by other code or pointer. For example the following program works fine.

int main(void)
{
    const volatile int local = 10;
    int *ptr = (int*) &local;
    printf("Initial value of local : %d \n", local);
    *ptr = 100;
    printf("Modified value of local: %d \n", local);
    return 0;
}

Write a program to print "hello world" without using a semicolon?

#include<stdio.h>
void main(){
 if(printf("hello world")){} // It prints the ?hello world? on the screen.
}

Write a program to swap two numbers without using the third variable?

#include<stdio.h>
#include<conio.h>
main()
{
int a=10, b=20;    //declaration of variables.
clrscr();        //It clears the screen.
printf("Before swap a=%d b=%d",a,b); 

a=a+b;//a=30 (10+20) 
b=a-b;//b=10 (30-20)
a=a-b;//a=20 (30-10)

printf("\nAfter swap a=%d b=%d",a,b);
getch();
}

Write a program to print Fibonacci series without using recursion?

#include<stdio.h>
#include<conio.h>
void main()
{
 int n1=0,n2=1,n3,i,number;
 clrscr();
 printf("Enter the number of elements:");
 scanf("%d",&number);
 printf("\n%d %d",n1,n2);//printing 0 and 1

 for(i=2;i<number;++i)//loop starts from 2 because 0 and 1 are already printed
 {
  n3=n1+n2;
  printf(" %d",n3);
  n1=n2;
  n2=n3;
 }
getch();
}