What will be the output of the program?

#include<stdio.h>
int reverse(int);

int main()
{
    int no=5;
    reverse(no);
    return 0;
}
int reverse(int no)
{
    if(no == 0)
        return 0;
    else
        printf("%d,", no);
    reverse (no--);
}

True, #undef can be used only on a macro that has been #define earlier

Example: #define PI 3.14

We can undefine PI macro by #undef PI

Rounding off a value means replacing it by a nearest value that is approximately equal or smaller or greater to the given number.

y = (int)(x + 0.5); here x is any float value. To roundoff, we have to typecast the value of x by using (int)

Example:

#include <stdio.h>

int main ()
{
  float x = 3.6;
  int y = (int)(x + 0.5);
  printf ("Result = %d\n", y );
  return 0;
}

Output:
Result = 4.

Declaration: char *fgets(char *s, int n, FILE *stream);

fgets reads characters from stream into the string s. It stops when it reads either n - 1 characters or a newline character, whichever comes first.

Therefore, the string str contain "I am a boy\n\0"

Linker Error : Undefined symbol 'i'
The statement extern int i specifies to the compiler that the memory for 'i' is allocated in some other program and that address will be given to the current program at the time of linking. But linker finds that no other variable of name 'i' is available in any other program with memory space allocated for it. Hence a linker error has occurred.

r+ Open an existing file for update (reading and writing).

During the for loop execution scanf() ask input and then printf() prints that given input. This process will be continued repeatedly because, scanf() returns the number of input given, the condition is always true(user gives a input means it reurns '1').

Hence this for loop would get executed infinite times.

Step 1: int y=128; The variable 'y' is declared as an integer type and initialized to value "128".

Step 2: const int x=y; The constant variable 'x' is declared as an integer and it is initialized with the variable 'y' value.

Step 3: printf("%d\n", x); It prints the value of variable 'x'.

Hence the output of the program is "128"

A function prototype in C or C++ is a declaration of a function that omits the function body but does specify the function's name, argument types and return type.

While a function definition specifies what a function does, a function prototype can be thought of as specifying its interface.

The macro PRINT(i) print("%d,", i); prints the given variable value in an integer format.

Step 1: int x=2, y=3, z=4; The variable x, y, z are declared as an integer type and initialized to 2, 3, 4 respectively.

Step 2: PRINT(x); becomes printf("%d,",x). Hence it prints '2'.

Step 3: PRINT(y); becomes printf("%d,",y). Hence it prints '3'.

Step 4: PRINT(z); becomes printf("%d,",z). Hence it prints '4'.

Hence the output of the program is 2, 3, 4.