What will be the output of the program?

#include<stdio.h>
void swap(char *, char *);

int main()
{
    char *pstr[2] = {"Hello", "CuriousTab"};
    swap(pstr[0], pstr[1]);
    printf("%s\n%s", pstr[0], pstr[1]);
    return 0;
}
void swap(char *t1, char *t2)
{
    char *t;
    t=t1;
    t1=t2;
    t2=t;
}

str[6] = "CURIOUSTAB"; - Nonportable pointer conversion.

The function strlen returns the number of characters in the given string.

Therefore, strlen("123456") returns 6.

Hence the output of the program is "6".

The function printf() returns the number of charecters printed on the console.

Step 1: char a[] = "\0"; The variable a is declared as an array of characters and it initialized with "\0". It denotes that the string is empty.

Step 2: if(printf("%s", a)) The printf() statement does not print anything, so it returns '0'(zero). Hence the if condition is failed.

In the else part it prints "The string is not empty".

The following examples may help you understand this problem:

1. sizeof("") returns 1 (1*).

2. sizeof("India") returns 6 (5 + 1*).

3. sizeof("CURIOUSTAB") returns 4 (3 + 1*).

4. sizeof("India\0CURIOUSTAB") returns 10 (5 + 1 + 3 + 1*).
    Here '\0' is considered as 1 char by sizeof() function.

5. sizeof("India\0CURIOUSTAB\0") returns 11 (5 + 1 + 3 + 1 + 1*).
    Here '\0' is considered as 1 char by sizeof() function.

Step 1: char *p1 = "India", *p2; The variable p1 and p2 is declared as an pointer to a character value and p1 is assigned with a value "India".

Step 2: p2=p1; The value of p1 is assigned to variable p2. So p2 contains "India".

Step 3: p1 = "CURIOUSTAB"; The p1 is assigned with a string "CURIOUSTAB"

Step 4: printf("%s %s\n", p1, p2); It prints the value of p1 and p2.

Hence the output of the program is "CURIOUSTAB India".

Step 1:

printf("%d, %d, %d", sizeof(3.0f), sizeof('3'), sizeof(3.0));

The sizeof function returns the size of the given expression.

sizeof(3.0f) is a floating point constant. The size of float is 4 bytes

sizeof('3') It converts '3' in to ASCII value.. The size of int is 2 bytes

sizeof(3.0) is a double constant. The size of double is 8 bytes

Hence the output of the program is 4,2,8

Note: The above program may produce different output in other platform due to the platform dependency of C compiler.

In Turbo C, 4 2 8. But in GCC, the output will be 4 4 8.

Here str[] has declared as 7 character array and into a 8 character is stored. This will result in overwriting of the byte beyond 7 byte reserved for '\0'.

Here fputc('A', fp1); stores 'A' in the file1.c then fputc('B', fp2); overwrites the contents of the file1.c with value 'B'. Because the fp1 and fp2 opens the file1.c in write mode.

Hence the file1.c contents is 'B'.