**C interview question**: What is a stack ?

**Answe**r: The stack is a region of memory within which our programs temporarily store data as they execute. For example, when a program passes parameters to functions, C places the parameters on the stack. When the function completes, C removes the items from the stack. Similarly, when a function declares local variables, C stores the variable's values on the stack during the function's execution. Depending on the program's use of functions and parameters, the amount of stack space that a program requires will differ.

**C interview question**:Allocating memory for a 3-D array

**Answer**: #include "alloc.h"

#define MAXX 3

#define MAXY 4

#define MAXZ 5

main( )

{

int ***p, i, j, k ;

p = ( int *** ) malloc ( MAXX * sizeof ( int ** ) ) ;

for ( i = 0 ; i < MAXX ; i++ )

{

p[i] = ( int ** ) malloc ( MAXY * sizeof ( int * ) ) ;

for ( j = 0 ; j < MAXY ; j++ )

p[i][j] = ( int * ) malloc ( MAXZ * sizeof ( int ) ) ;

}

for ( k = 0 ; k < MAXZ ; k++ )

{

for ( i = 0 ; i < MAXX ; i++ )

{

for ( j = 0 ; j < MAXY ; j++ )

{

p[i][j][k] = i + j + k ;

printf ( "%d ", p[i][j][k] ) ;

}

printf ( "\n" ) ;

}

printf ( "\n\n" ) ;

}

}

**C interview question**:How to distinguish between a binary tree and a tree?

**Answer**: A node in a tree can have any number of branches. While a binary tree is a tree structure in which any node can have at most two branches. For binary trees we distinguish between the subtree on the left and subtree on the right, whereas for trees the order of the subtrees is irrelevant.

Consider two binary trees, but these binary trees are different. The first has an empty right subtree while the second has an empty left subtree. If the above are regarded as trees (not the binary trees), then they are same despite the fact that they are drawn differently. Also, an empty binary tree can exist, but there is no tree having zero nodes.

**C interview question**:How do I use the function ldexp( ) in a program?

**Answer**: The math function ldexp( ) is used while solving the complex mathematical equations. This function takes two arguments, a double value and an int respectively. The order in which ldexp( ) function performs calculations is ( n * pow ( 2, exp ) ) where n is the double value and exp is the integer. The following program demonstrates the use of this function.

#include

void main( )

{

double ans ;

double n = 4 ;

ans = ldexp ( n, 2 ) ;

printf ( "\nThe ldexp value is : %lf\n", ans ) ;

}

Here, ldexp( ) function would get expanded as ( 4 * 2 * 2 ), and the output would be the ldexp value is : 16.000000

**C interview question**:Can we get the mantissa and exponent form of a given number?

**Answer**:The function frexp( ) splits the given number into a mantissa and exponent form. The function takes two arguments, the number to be converted as a double value and an int to store the exponent form. The function returns the mantissa part as a double value. Following example demonstrates the use of this function.

#include

void main( )

{

double mantissa, number ;

int exponent ;

number = 8.0 ;

mantissa = frexp ( number, &exponent ) ;

printf ( "The number %lf is ", number ) ;

printf ( "%lf times two to the ", mantissa ) ;

printf ( "power of %d\n", exponent ) ;

return 0 ;

}

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