Output of C programs | Set 60 (Constants)

Prerequisite : C Constants and Strings
Q.1 What is the output of this program? 

CPP

#include<iostream>
using namespace std;
int main()
{
    const char *s = "";
    char str[] = "Hello";
    s = str;
    while(*s)
        printf("%c", *s++);

    return 0;
}

Options
a) Error 
b) H 
c) Hello 
d) Hel 

ans:- c 

Explanation : 

 const char *s = "";

The constant variable s is declared as an pointer to an array of characters type and initialized with an empty string. 

char str[] = "Hello"; 

The variable str is declared as an array of characters type and initialized with a string “Hello”. 

s = str;

The value of the variable str is assigned to the variable s. Therefore str contains the text “Hello”.

while(*s)
{ printf("%c", *s++); } 

Here the while loop got executed until the value of the variable s is available and it prints the each character of the variable s. 
Hence the output of the program is “Hello”.
Q.2 What is the output of this program? 

CPP

#include<iostream>
using namespace std;
int get();

int main()
{
    const int x = get();
    printf("%d", x);
    return 0;
}
int get()
{
    return 20;
}

Options
a) Garbage value 
b) Error 
c) 20 
d) 0 

ans:- c

Explanation : 

int get(); 

This is the function prototype for the function get(), it tells the compiler returns an integer value and accept no parameters. 

const int x = get(); 

The constant variable x is declared as an integer data type and initialized with the value “20”. 
The function get() returns the value “20”.
Q.3 What is the output of this program? 

CPP

#include<iostream>
using namespace std;
int fun(int **ptr);

int main()
{
    int i=10;
    const int *ptr = &i;
    fun(&ptr);
    return 0;
}
int fun(int **ptr)
{
    int j = 223;
    int *temp = &j;
    printf("Before changing ptr = %5x\n", *ptr);
    const *ptr = temp;
    printf("After changing ptr = %5x\n", *ptr);
    return 0;
}

Options
a) Address of i 
Address of j 
b) 10 
223 
c) Error: cannot convert parameter 1 from ‘const int **’ to ‘int **’ 
d) Garbage value

ans:- c

Explanation : Here ptr is declared as constant integer pointer to which address of i is assigned but in function fun double pointer is passed as an argument, so it can’t convert from ‘const int **’ to ‘int **’.
Q.4 What is the output of this program? 

CPP

#include<iostream>
using namespace std;
int main()
{
    const int i=0;
    printf("%d\n", i++);
    return 0;
}

Options
a) 10 
b) 11 
c) No output 
d) Error: ++needs a value 

ans:- d

Explanation : 

const int i = 0; 

The constant variable ‘i’ is declared as an integer and initialized with value of ‘0’(zero). 

printf("%d\n", i++); 

Here the variable ‘i’ is incremented by 1(one). This will create an error “Cannot modify a const object”. 
Because, we cannot modify a const variable.
Q.5 What is the output of this program? 

CPP

#include<iostream>
using namespace std;
int main()
{
    const int c = -11;
    const int d = 34;
    printf("%d, %d\n", c, d);
    return 0;
}

Options
a) Error 
b) -11, 34 
c) 11, 34 
d) None of these 

ans:- b

Explanation :- 

const c = -11;

The constant variable ‘c’ is declared and initialized to value “-11”. 

const int d = 34;

The constant variable ‘d’ is declared as an integer and initialized to value ’34’. 

printf("%d, %d\n", c, d); 

The value of the variable ‘c’ and ‘d’ are printed. 
Hence the output of the program is -11, 34
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