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# c basics interview questions and answers

1
Which of the below are not valid in C?
1. class aClass{public: int x;};
2. /* Comment A */
3. char ar=253;
4. none of the above
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2
what does below code do in c?

a ^= b^ = a^ = b;
1. it will swap the values of a and b
2. it will swap addresses of a and b
3. it doubles the values of a and b
4. it jumbles values of a and b, but finally it will not be swapped.
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3
Write a program to print hello world with out using semicolon, by using a c program.
1. main()
{
if(printf(”Hello world”));
}
2. main()
{
printf(”Hello world”)
}
3. main()
{
if(printf(”Hello world”))
{
}
}
4. It is not possible to write c program with out a semicolor ;
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4
Example of for loop and arrays in c:

What is below program doing?

int hack(int n)
{
int f[n+1];
f[1] = f[2] = 1;

printf("\nf[1] = %d", f[1]);
printf("\nf[2] = %d", f[2]);
for (int i = 3; i <= n; i++)
{
f[i] = f[i-1] + f[i-2];
printf("\nf[%d] = [%d]",i,f[i]);
}
return f[n];
}
1. This is a recursive way to find fibonacci series.
2. this program will end up in infinite for loop and crashes.
3. This is an iterative way to find the factorial of a given number.
4. an iterative way to generate fibonacci numbers and also return the nth number.
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5
How to swap 2 variables with out using temporary variable by using a c program?
1. a=a+b; b=a-b; a=a-b;
2. a^ = b^ = a^ = b; We can use ^ (x-or) symbol and do some trick to swap two values. But this technique won't work with some compiler implementations.
3. both are correct
4. both are wrong
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6
while loop with example in c:

What is the output of below program? what is this program doing?

int main()
{
int num = 15;
int r=0;
while(num)
{
r=r*10+num%10;
num=num/10;
}
printf(" %d",r);

return 0;
}
1. This is the code to reverse a given number, output will be 51 for this program.
2. this code finds whether the given number is divisible by 10 or not. it prints 15.
3. this code finds whether the given number is multiple of 10 or not. it prints 0.
4. this code finds whether the given number is divisible by 10 or not. it prints 51.
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12
What does 7/9*9 equals in c?
1. 1
2. 0.08642
3. 0
4. none of the above
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13
Evaluate the following statement in c:

!(1&&0||!1)
1. TRUE
2. FALSE
3. invalid expression
4. depends on the compiler
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18
What does below code will do?

int a=5 ,b=7,c ;
c=a+++b ;
1. a=5;b=7;c=12
2. a=6;b=7;c=12
3. a=6;b=7;c=13
4. error
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19
Is the following c code correct?

const int i=9;
int &r=i;
1. yes
2. no
3. depends on compiler
4. compile time error
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20
What is the mistake with below c program? If there is no mistake, then what is the output?

main()
{
int i=10;
printf("%d",(i++*i++))
}
1. Even though it works, it is not a proper way to use same variable which varies its value in the same expression.
2. 122
3. 100
4. 120