Consider the following ANSI-C program.
#include <stdio.h>
int main(){
int *ptr, a, b, c;
a=5; b=11; c=20;
ptr=&a; *ptr=c; ptr=&c;
a=*(&b); c=*ptr-a;
printf("%d",c);
return(0);
}
The output of this program is ____________. (answer in integer)
Note: Assume that the program compiles and runs successfully.
C Program Output: Step-by-Step Execution Analysis
We trace the values of variables $a$, $b$, $c$, and the pointer $ptr$ throughout the program execution.
Initial Variable Values
- $a = 5$
- $b = 11$
- $c = 20$
- $ptr$ is uninitialized.
Pointer Assignments and Dereferencing
- $ptr = &a;$: The pointer $ptr$ now holds the memory address of variable $a$.
- $*ptr = c;$: The value of $c$ (which is 20) is assigned to the memory location pointed to by $ptr$. Since $ptr$ points to $a$, variable $a$ is updated.
- $a$ becomes 20.
- $ptr = &c;$: The pointer $ptr$ now holds the memory address of variable $c$.
- $a = *(&b);$: This expression retrieves the value stored at the memory address of $b$ (which is 11) and assigns it to $a$.
- $a$ becomes 11.
- $c = *ptr - a;$:
- $*ptr$ dereferences $ptr$, which points to $c$. So, $*ptr$ evaluates to the current value of $c$ (20).
- The expression becomes $c = 20 - a$.
- Substituting the current value of $a$ (11), we get $c = 20 - 11$.
- $c$ becomes 9.
Final Output
The $printf("%d", c);$ statement prints the final value of $c$.
- The final value of $c$ is $9$.
Therefore, the program outputs $9$.
Important Questions from Pointer
What is the output of the following C programming language code?
#include<stdio.h>
int main()
{
int x = 10;
int *p = &x;
*p = *p + 5;
printf("%d %d", x, *p);
return 0;
}
- The following statement in ‘C’
int (*f())[ ];
declares - What would be the equivalent pointer expression for referring the array element ar[m][n][o]
- Only legal pointer operations:
A. pointer + number $\rightarrow$ pointer
B. pointer - number $\rightarrow$ number
C. pointer + pointer $\rightarrow$ pointer
D. pointer - pointer $\rightarrow$ pointer
E. pointer - pointer $\rightarrow$ number
Choose the most appropriate answer from the options given below: What is the output of the following program ?
(Assume that the appropriate preprocessor directives are included and there is no syntax error)
main ( )
{ char S[ ]="ABCDEFGH";
printf ("%C", * (& S[3]));
printf ("%s", S+4);
printf ("%u", S);
/* Base address of S is 1000 */
}
