Introduction to programming language C Some sorts of questions
1. What is the difference between declaration and definition of a variable/function?
Solution: Declaration of a variable/function simply declares that the variable/function exists somewhere in the program but the memory is not allocated for them. When a variable is declared, the program knows the data type of that variable. In case of functions, their data types, the order of arguments and the return type. When we define a variable /function, apart from the role of declaration, it also allocates memory for that variable/functions. Declaration can be any number of times but definition only one time.
extern int I; //only declaration int x; //both definition and declaration 2. What are different storage class specifies in C?
auto,register,static,extern.
3. When should we use pointers in a C program?
a. To get address of a variable.
b. For achieving pass by reference in c.
c. To pass large structures.
d. To implement linked data structures.
4. What is a NULL pointer?
It is a pointer that doesn’t point to a valid location. At the time of declaration we don’t know the value. So it can initialize as NULL.
5. What is a dangling pointer?
It is a pointer that doesn’t point to a valid memory. Dangling pointer arise when an object is deleted or de-allocated, without modifying the value of the pointer, so that the pointer still points to the memory location of the de-allocated memory.
int *ptr=(int *)malloc(sizeof(int));
free(ptr);
*ptr=10; //it’s a dangling reference 6. What is memory leak?
Memory leak occurs when programmers create a memory in heap and forget to delete it.
void func(){
int *ptr=(int *)malloc(sizeof(int));
return;
}
7. What are local static variables? What is their use?
A local static variable is a variable whose lifetime doesn’t end with a function call where it is declared. It extends for the lifetime of complete program. All calls to the function share the same copy of local static variables. It is used to count the number of function call. It’s default value is 0.
#include<stdio.h>
void func(){
static int x;
printf(“%d”,x);
x=x+1;
}
Int main(){
func();
func();
}
Output::01 8. Static function
It has a scope that is limited to its object file. It Is only visible in its object file. It is restricted to access.
First.c
static void st(void){
printf(“this”);
}
Second.c int main(){
st();
}
This will cause an error.
9. Difference between ++*p,*p++,*++p.
Associativity right to left and need precedence.
++*p=++(*p)
*p++=*(p++)
*++p=*(++p)
10. What is l-value and r-value?
l-value or location value refers to an expression that can be used on left side of assignment operator.
A=3;
l-value=A r-value=3
l-value can be modifiable or non-modifiable(constant).
11. What is a pointer on pointer?
It’s a pointer variable which can hold the address of another pointer variable.
int x=5, *p=&x,**q=&p;
12. Distinguish between malloc() and calloc().
Both allocates memory from heap area/dynamic memory. By default, calloc() fills the allocated memory with 0’s.
13. What is keyword auto for?
By default, every local variable is automatic(auto).
auto int I;
int j;
//both are auto
14. extern is used to resolve the global scope.
int main(){
extern int I;
printf(“this”);
} int i=20;
15. if a variable is used most frequently then use register for using CPU register.
register int i=10;
16. Purposes of typedef.
Alias the existing type. Simplify the complex declaration type.
17. Can a program be compiled without main() function?
Yes, compiled but not execute.
18. %i all supported format can input.
19. “\” means escape.
20. FILE is not built-in-data type, it is structure in stdio 21. Type casting is conversion of one type to another.
int x=10;
float y=(float)x;
22. <> is used to go to built in include path for searching
“ “ search in current folder then built in include path.
23. Printf(),scanf() return integer how many character it successfully print.
