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C Interview Questions And Answers - Part 2.

What is printf()?
Answer: printf() is an inbuilt library function in C library by default. This function is declared and related macros are defined in “stdio.h” header file. printf() function is used to print the “character, string, float, integer, octal and hexadecimal values” onto the output screen.

What is scanf()?
Answer: scanf() is an inbuilt library function in C library by default. This function is declared and related macros are defined in “stdio.h” header file. scanf() function is used to read character, string, numeric data from keyboard.

What is void in C?
Answer: Void is an empty data type that has no value. We use void data type in functions when we don’t want to return any value to the calling function.

Example: void sum (int a, int b); – This function won’t return any value to the calling function.

int sum (int a, int b); – This function will return value to the calling function.

We use void data type in pointer like “void *p”. It means, pointer “p” is neither pointing to int data type nor char data type. It acts as generic pointer. We are using void pointer when we are not sure on the data type that this pointer will point to. We can use void pointer to refer either integer data or char data. But, this void pointer should not be dereferenced without explicit type casting.

We use void in functions as “int function_name (void)”. Here void means, this function does not pass any argument.

What is token in C? What are the types of C tokens?
Answer: Tokens are the basic buildings blocks which are constructed together to write a program. Any smallest individual unit in a C program are known as tokens. C tokens are of six types. They are:

Keywords                        (eg: int, while),
Identifiers                       (eg: main, total),
Constants                       (eg: 10, 20),
Strings                            (eg: “total”, “hello”),
Special symbols               (eg: (), {}),
Operators                        (eg: +, /,-,*)

How will you print “Hello World” without semicolon?
Answer:
Solution: 1

#include<stdio.h>
void main(){
if(printf("Hello world")){
}}

Solution: 2

#include<stdio.h>
void main(){
while(!printf("Hello world")){
}}

Solution: 3

#include<stdio.h>
void main(){
switch(printf("Hello world")){
}}

Swap two variables without using third variable.

#include<stdio.h>
int main() {
int a=5, b=10;

// process one
a=b+a;
b=a-b;
a=a-b;
printf("a = %d  b =  %d",a,b);

// process two
a=5;
b=10;
a=a+b-(b=a);
printf("\na = %d  b =  %d",a,b);

// process three
a=5;
b=10;
a=a^b;
b=a^b;
a=b^a;
printf("\na = %d  b =  %d",a,b);

// process four
a=5;
b=10;
a=b-~a-1;
b=a+~b+1;
a=a+~b+1;
printf("\na = %d  b =  %d",a,b);

// process five
a=5,
b=10;
a=b+a,b=a-b,a=a-b;
printf("\na = %d  b =  %d",a,b);

return 0;
}

Can the “if” function be used in comparing strings?
Answer: No. “if” command can only be used to compare numerical values and single character values. For comparing string values, there is another function called strcmp that deals specifically with strings.

What is the outcome of following statement if the value of s is 10?
s >=10 && s < 25 && s!=12
Answer: The outcome will be TRUE. Since the value of s is 10, s >= 10 evaluates to TRUE because s is not greater than 10 but is still equal to 10. s< 25 is also TRUE since 10 is less than 25. Just the same, s!=12, which means s is not equal to 12, evaluates to TRUE. The && is the AND operator, and follows the rule that if all individual conditions are TRUE, the entire statement is TRUE.

What is keyword? List out some keywords available in C language.
Answer: Keywords are pre-defined words in a C compiler. Each keyword is meant to perform a specific function in a C program. Since keywords are referred names for compiler, they cannot be used as variable name.

Below are some of keywords that C language offers:
auto, double, int, struct, break, else, long, switch, case, enum, register, typedef, char, extern, return, union, const, float, short, unsigned, continue, for, signed, void, default, goto, sizeof, volatile, do, if, static, while.

Can variable name start with numbers?
Answer: No, variable names cannot start with numbers as per the variable naming rule.
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