C Interview Questions - Set 1

This page consists of C Programming interview questions and answers.

Q1: Who created C?

Dennis Ritchie is the creator of the C programming language. Brian Kernighan also contributed in the development of the language.

Q2: Using for loop print the following pattern in C programming language

Pattern:

*
1 2
* * *
1 2 3 4
* * * * *

Answer:

For this we can write the following C code.

int r, c, rLim;
rLim = 5;
for (r = 0; r < rLim; r++) {
  for (c = 1; c <= r + 1; c++) {
    if (r % 2 == 0) {
      printf("* ");
    } else {
      printf("%d ", c);
    }
  }
  printf("\n");
}

So, for the even rows we are printing * and for the odd rows we are printing numbers.

Click here to check out the for loop tutorial in C programming.

Q3: What are static variables in C programming?

Static variable are the variables that retain their value.

If we have a static variable inside a function then it will retain its value between function calls.

Q4: What is the default value for a static variable in C?

The default value for a static variable is 0.

Q5: Write the output of the following C program

Program:

#include <stdio.h>

void printNumber();

int main(void) {
  printNumber();
  printNumber();
  printNumber();

  return 0;
}

void printNumber() {
  static int n;
  printf("n = %d\n", n);
  n++;
}

Answer:

Following is the output of the above code.

n = 0
n = 1
n = 2

Since, n is a static variable so the default value assigned to it is 0.

We are making 3 function calls to printNumber() function.

During the 1st call n is 0. Then we increment its value by 1 using the increment operator ++. So, the value becomes 1.

In the 2nd call n is 1 then its value is incremented by 1.

In the 3rd call n is 2 and its value is incremented by 1 so, n becomes 3.

Since, we are making 3 calls so we get 0, 1 and 2.

Q6: Write the output of the following C program

C program:

int i = 10;
while (i) {
  printf("i = %d\n", i++);
  i -= 3;
}

Answer:

The above code will give us the following output.

i = 10
i = 8
i = 6
i = 4
i = 2

We are starting with i = 10. Then we are entering the while loop.

Inside the loop we are printing the value of i and in the printf statement we are incrementing the value of i by 1 using the increment operator.

Note! The value is first used then incremented.

So, i = 10 is printed then i is incremented by 1 and it becomes 11.

After printf the value of i is decreased by 3. So, i becomes 8.

So, for the next loop the value of i is 8. And this continues till value of i is not equal to 0.

When i becomes 0 we exit the loop.

Click here to learn more about while loop in C.

Q7: Write C program to print the ASCII code of the message "Hello World"

C code:

#include <stdio.h>

int main(void) {
  char message[] = "Hello World";
  int i;
  for (i = 0; message[i] != '\0'; i++) {
    printf("ASCII code of %c = %d\n", message[i], message[i]);
  }
}

Q8: What will be the output of the following C program?

C program:

int x = 10;
int *p = &x;
*p = 20;
printf("x = %d", x);

Answer:

The above code will print x = 20.

In the above code x is assigned an interger value 10. Then its address is saved in the pointer variable p.

Next, the value of x is set to 20 via the pointer. And finally, the new value of x is printed out.

Click here to learn more about Pointers in C.

Q9: Write C code to print the first 10 numbers of the Fibonacci series

C program to print first 10 numbers of the Fibonacci series.

#include <stdio.h>

int main(){
  int count = 10;
  int i;
  int prev = 1;
  int curr = 1;
  int next;
  printf ("%d %d ", prev, curr);
  for (i = 3; i <= count; i++) {
    next = prev + curr;
    printf("%d ", next);
    prev = curr;
    curr = next;
  }
  printf("\n");
  return 0;
}

Output:

1 1 2 3 5 8 13 21 34 55

Click here to check out Fibonacci video tutorial.

Q10: Write C code to check if an entered word is a Palindrome

C code:

#include <stdio.h>
#include <string.h>

int main(){
  char str[100];
  int beginIdx, endIdx;
  int isPalindrome = 1;
  
  //input
  printf("Enter string [max 99 characters]: ");
  scanf("%s", str);

  for (beginIdx = 0, endIdx = strlen(str) - 1; beginIdx < endIdx; beginIdx++, endIdx--) {
    if (str[beginIdx] != str[endIdx]) {
      isPalindrome = 0;
      break;
    }
  }

  if (isPalindrome) {
    printf("%s is a Palindrome word.\n", str);
  } else {
    printf("%s is not a Palindrome word.\n", str);
  }
   
  return 0;
}

Some of the palindrome words are: level, noon, radar, refer, madam.

Click here to check out the video tutorial on Palindrome.