IndiaBIX

C Programming - Const

Exercise : Const - Point Out Errors
1.
Point out the error in the program. 
#include<stdio.h>
#define MAX 128

int main()
{
    char mybuf[] = "India";
    char yourbuf[] = "BIX";
    char *const ptr = mybuf;
    *ptr = 'a';
    ptr = yourbuf;
    return 0;
}
Error: unknown pointer conversion
Error: cannot convert ptr const value
No error
None of above
Answer: Option
Explanation:

Step 1: char mybuf[] = "India"; The variable mybuff is declared as an array of characters and initialized with string "India".

Step 2: char yourbuf[] = "BIX"; The variable yourbuf is declared as an array of characters and initialized with string "BIX".

Step 3: char *const ptr = mybuf; Here, ptr is a constant pointer, which points at a char.

The value at which ptr it points is not a constant; it will not be an error to modify the pointed character; There will be an error only to modify the pointer itself.

Step 4: *ptr = 'a'; The value of ptr is assigned to 'a'.

Step 5: ptr = yourbuf; Here, we are changing the pointer itself, this will result in the error "cannot modify a const object".

2.
Point out the error in the program (in Turbo-C). 
#include<stdio.h>
#define MAX 128

int main()
{
    const int max=128;
    char array[max];
    char string[MAX];
    array[0] = string[0] = 'A';
    printf("%c %c\n", array[0], string[0]);
    return 0;
}
Error: unknown max in declaration/Constant expression required
Error: invalid array string
None of above
No error. It prints A A
Answer: Option
Explanation:

Step 1: A macro named MAX is defined with value 128

Step 2: const int max=128; The constant variable max is declared as an integer data type and it is initialized with value 128.

Step 3: char array[max]; This statement reports an error "constant expression required". Because, we cannot use variable to define the size of array.

To avoid this error, we have to declare the size of an array as static. Eg. char array[10]; or use macro char array[MAX];

Note: The above program will print A A as output in Unix platform.

3.
Point out the error in the program. 
#include<stdio.h>
#include<stdlib.h>

union employee
{
    char name[15];
    int age;
    float salary;
};
const union employee e1;

int main()
{
    strcpy(e1.name, "K");
    printf("%s", e1.name);    
    e1.age=85;
    printf("%d", e1.age);
    printf("%f", e1.salary);
    return 0;
}
Error: RValue required
Error: cannot modify const object
Error: LValue required in strcpy
No error
Answer: Option
Explanation:
No answer description is available. Let's discuss.
4.
Point out the error in the program. 
#include<stdio.h>
const char *fun();

int main()
{
    char *ptr = fun();
    return 0;
}
const char *fun()
{
    return "Hello";
}
Error: Lvalue required
Error: cannot convert 'const char *' to 'char *'.
No error and No output
None of above
Answer: Option
Explanation:
No answer description is available. Let's discuss.
5.
Point out the error in the program. 
#include<stdio.h>

int main()
{
    const int x;
    x=128;
    printf("%d\n", x);
    return 0;
}
Error: unknown data type const int
Error: const variable have been initialised when declared.
Error: stack overflow in x
No error
Answer: Option
Explanation:

A const variable has to be initialized when it is declared. later assigning the value to the const variable will result in an error "Cannot modify the const object".

Hence Option B is correct

Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers