Coding Interview Questions In C

March 17, 2021

Top Coding Interview Questions In C

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coding interview questions in c

Learn c : Introduction

C is a common high-level programming language among programmers because it is the most compatible, simple to understand, and powerful programming language. It is the successor to the B programming language, which first appeared in the 1970s and has been the most popular programming language ever since.

Features of C programming:-

  • C is a Middle level language. 
  • It is case sensitive.
  • It is easy to extend.
  • Highly portable.
  • It is fast and efficient.
  • It is more widely used language in operating systems and embedded system.
  • It is the simple language.
Basics of C

Few Important Pages to be Checked:

Commonly Asked Coding Interview Questions In C

1.Display Prime Numbers Between Two Intervals.

Solution:-

#include <stdio.h>

int main() {
   int low, high, i, flag;
   printf("Enter two numbers(intervals): ");
   scanf("%d %d", &low, &high);
   printf("Prime numbers between %d and %d are: ", low, high);

   // iteration until low is not equal to high
   while (low < high) {
      flag = 0;

      // ignore numbers less than 2
      if (low <= 1) {
         ++low;
         continue;
      }

      // if low is a non-prime number, flag will be 1
      for (i = 2; i <= low / 2; ++i) {

         if (low % i == 0) {
            flag = 1;
            break;
         }
      }

      if (flag == 0)
         printf("%d ", low);

      // to check prime for the next number
      // increase low by 1
      ++low;
   }

OUTPUT

Enter two numbers(intervals): 20
50
Prime numbers between 20 and 50 are: 23 29 31 37 41 43 47

2.Write a C Program to Print Pyramids and Patterns.

*
* *
* * *
* * * *
* * * * *
Solution:- 
#include <stdio.h>

int main() {

int i, j, rows;

printf("Enter the number of rows: ");

scanf("%d", &rows);

for (i = 1; i <= rows; ++i) {

for (j = 1; j <= i; ++j) {

printf("* ");

}

printf("\n");

}
return 0;

}

3.Write a C Program to Find the Sum of Natural Numbers using Recursion.

Solution:-
#include
Numbers(int n);

int main() {

int num;

printf("Enter a positive integer: ");

scanf("%d", &num);

printf("Sum = %d", addNumbers(num));

return 0;

}

int addNumbers(int n) {

if (n != 0)

return n + addNumbers(n - 1);

else

return n;

}

OUTPUT

Enter a positive integer: 20
Sum = 210

4.Write a C Program to Find Largest Element in an Array.

Solution:-
#include<stdio.h>
int main() {
int i, n;
float arr[100];
printf("Enter the number of elements (1 to 100): ");
scanf("%d", &n);

for (i = 0; i < n; ++i) {
printf("Enter number%d: ", i + 1);
scanf("%f", &arr[i]);
}

// storing the largest number to arr[0]
for (i = 1; i < n; ++i) {
if (arr[0] < arr[i])
arr[0] = arr[i];
}

printf("Largest element = %.2f", arr[0]);

return 0;
}

OUTPUT

Enter the number of elements (1 to 100): 5
Enter number1: 34.5
Enter number2: 2.4
Enter number3: -35.5
Enter number4: 38.7
Enter number5: 24.5
Largest element = 38.70

5.Write a C Program to Add Two Matrices Using Multi-dimensional Arrays

Solution:-

#include<stdio.h> 
int main() {
int r, c, a[100][100], b[100][100], sum[100][100], i, j;
printf("Enter the number of rows (between 1 and 100): ");
scanf("%d", &r);
printf("Enter the number of columns (between 1 and 100): ");
scanf("%d", &c);

printf("\nEnter elements of 1st matrix:\n");
for (i = 0; i < r; ++i)
for (j = 0; j < c; ++j) {
printf("Enter element a%d%d: ", i + 1, j + 1);
scanf("%d", &a[i][j]);
}

printf("Enter elements of 2nd matrix:\n");
for (i = 0; i < r; ++i)
for (j = 0; j < c; ++j) {
printf("Enter element a%d%d: ", i + 1, j + 1);
scanf("%d", &b[i][j]);
}

// adding two matrices
for (i = 0; i < r; ++i)
for (j = 0; j < c; ++j) {
sum[i][j] = a[i][j] + b[i][j];
}

// printing the result
printf("\nSum of two matrices: \n");
for (i = 0; i < r; ++i)
for (j = 0; j < c; ++j) {
printf("%d ", sum[i][j]);
if (j == c - 1) {
printf("\n\n");
}
}
return 0;
}

OUTPUT

Enter the number of rows (between 1 and 100): 2
Enter the number of columns (between 1 and 100): 3

Enter elements of 1st matrix:
Enter element a11 : 2
Enter element a12 : 3
Enter element a13 : 4
Enter element a21 : 5
Enter element a22 : 2
Enter element a23  : 3
Enter elements of 2nd matrix:
Enter element a11 : -4
Enter element a12 : 5
Enter element a13 : 3
Enter element a21 : 5
Enter element a22 : 6
Enter element a23 : 3

Sum of two matrices:
-2    8     7

10    8     6

6.Write a Program Remove Characters in String Except Alphabets.

Solution:-

#include 
int main() {
char line[150];

printf("Enter a string: ");
fgets(line, sizeof(line), stdin); // take input


for (int i = 0, j; line[i] != '\0'; ++i) {

// enter the loop if the character is not an alphabet
// and not the null character
while (!(line[i] >= 'a' && line[i] <= 'z') && !(line[i] >= 'A' && line[i] <= 'Z') && !(line[i] == '\0')) {
for (j = i; line[j] != '\0'; ++j) {

// if jth element of line is not an alphabet,
// assign the value of (j+1)th element to the jth element
line[j] = line[j + 1];
}
line[j] = '\0';
}
}
printf("Output String: ");
puts(line);
return 0;
}

OUTPUT

Enter a string: p2’[email protected]/
Output String: programiz

7. Write a C Program to Find the Length of a String.

Solution:-

#include 
int main() {
char s[] = "Programming is fun";
int i;

for (i = 0; s[i] != '\0'; ++i);

printf("Length of the string: %d", i);
return 0;
}

OUTPUT

Length of the string: 18

8. Write a C Program to Calculate Difference Between Two Time Periods

Solution:-

#include 
struct TIME {
int seconds;
int minutes;
int hours;
};

void differenceBetweenTimePeriod(struct TIME t1,
struct TIME t2,
struct TIME *diff);

int main() {
struct TIME startTime, stopTime, diff;

printf("Enter the start time. \n");
printf("Enter hours, minutes and seconds: ");
scanf("%d %d %d", &startTime.hours,
&startTime.minutes,
&startTime.seconds);

printf("Enter the stop time. \n");
printf("Enter hours, minutes and seconds: ");
scanf("%d %d %d", &stopTime.hours,
&stopTime.minutes,
&stopTime.seconds);

// Difference between start and stop time
differenceBetweenTimePeriod(startTime, stopTime, &diff);
printf("\nTime Difference: %d:%d:%d - ", startTime.hours,
startTime.minutes,
startTime.seconds);
printf("%d:%d:%d ", stopTime.hours,
stopTime.minutes,
stopTime.seconds);
printf("= %d:%d:%d\n", diff.hours,
diff.minutes,
diff.seconds);
return 0;
}

// Computes difference between time periods
void differenceBetweenTimePeriod(struct TIME start,
struct TIME stop,
struct TIME *diff) {
while (stop.seconds > start.seconds) {
--start.minutes;
start.seconds += 60;
}
diff->seconds = start.seconds - stop.seconds;
while (stop.minutes > start.minutes) {
--start.hours;
start.minutes += 60;
}
diff->minutes = start.minutes - stop.minutes;
diff->hours = start.hours - stop.hours;
}

OUTPUT

Enter the start time.
Enter hours, minutes and seconds: 12
34
55
Enter the stop time.
Enter hours, minutes and seconds: 8
12
15

Time Difference: 12:34:55 – 8:12:15 = 4:22:40

9. Write a C Program to Find Largest Number Using Dynamic Memory Allocation

Solution:-

#include 
int main() {
int num;
float *data;
printf("Enter the total number of elements: ");
scanf("%d", &num);

// Allocating memory for num elements
data = (float *)calloc(num, sizeof(float));
if (data == NULL) {
printf(“Error!!! memory not allocated.”);
exit(0);
}

// Storing numbers entered by the user.
for (int i = 0; i < num; ++i) {
printf(“Enter Number %d: “, i + 1);
scanf(“%f”, data + i);
}

// Finding the largest number
for (int i = 1; i < num; ++i) {
if (*data < *(data + i))
*data = *(data + i);
}
printf(“Largest number = %.2f”, *data);

return 0;
}

10. Write a C Program to Access Array Elements Using Pointer

Solution:-

#include <stdio.h>
int main() {
int data[5];

printf("Enter elements: ");
for (int i = 0; i < 5; ++i)
scanf("%d", data + i);

printf("You entered: \n");
for (int i = 0; i < 5; ++i)
printf("%d\n", *(data + i));
return 0;
}

OUTPUT

Enter elements: 1
2
3
5
4
You entered:
1
2
3
5
4

11. Write a C Program to Find the Transpose of a Matrix.

#include 
int main() {
int a[10][10], transpose[10][10], r, c, i, j;
printf("Enter rows and columns: ");
scanf("%d %d", &r, &c);

// Assigning elements to the matrix
printf("\nEnter matrix elements:\n");
for (i = 0; i < r; ++i)
for (j = 0; j < c; ++j) {
printf("Enter element a%d%d: ", i + 1, j + 1);
scanf("%d", &a[i][j]);
}

// Displaying the matrix a[][]
printf("\nEntered matrix: \n");
for (i = 0; i < r; ++i)
for (j = 0; j < c; ++j) {
printf("%d ", a[i][j]);
if (j == c - 1)
printf("\n");
}

// Finding the transpose of matrix a
for (i = 0; i < r; ++i)
for (j = 0; j < c; ++j) {
transpose[j][i] = a[i][j];
}

// Displaying the transpose of matrix a
printf("\nTranspose of the matrix:\n");
for (i = 0; i < c; ++i)
for (j = 0; j < r; ++j) {
printf("%d ", transpose[i][j]);
if (j == r - 1)
printf("\n");
}
return 0;
}

OUTPUT

Enter rows and columns: 2
3

Enter matrix elements:
Enter element a11: 1
Enter element a12: 4
Enter element a13: 0
Enter element a21: -5
Enter element a22: 2
Enter element a23: 7

Entered matrix:
1  4  0
-5  2  7

Transpose of the matrix:
1  -5
4  2
0  7

12. Write a Bubble Sort program.

Solution :-   
int main()
{
      int array[100], n, i, j, swap; 
      printf("Enter number of elementsn");
      scanf("%d", &n); 
      printf("Enter %d Numbers:n", n); 
      for(i = 0; i<n; i++)
           scanf("%d", &array[i]); 
           for(i = 0 ; i<n - 1; i++)
           {
                 for(j = 0 ; j < n-i-1; j++) { if(array[j]>array[j+1]) 
                       {
                               swap=array[j];
                               array[j]=array[j+1];
                               array[j+1]=swap;
                       }
                 }
           } 
           printf("Sorted Array:n"); 
           for(i = 0; i < n; i++)
                 printf("%dn", array[i]);
           return 0;
}

13. Write a C Program to Convert Binary Number to Octal and vice-versa.

Solution:-

#include<math.h>
#include<stdio.h>
int convert(long long bin);
int main() {
long long bin;
printf("Enter a binary number: ");
scanf("%lld", &bin);
printf("%lld in binary = %d in octal", bin, convert(bin));
return 0;
}

int convert(long long bin) {
int oct = 0, dec = 0, i = 0;

// converting binary to decimal
while (bin != 0) {
dec += (bin % 10) * pow(2, i);
++i;
bin /= 10;
}
i = 1;

// converting to decimal to octal
while (dec != 0) {
oct += (dec % 8) * i;
dec /= 8;
i *= 10;
}
return oct;
}

OUTPUT

Enter an octal number: 67
67 in octal = 110111 in binary

14.Write a C program to Reverse a Sentence Using Recursion

#include <stdio.h>
void reverseSentence();
int main() {
printf("Enter a sentence: ");
reverseSentence();
return 0;
}

void reverseSentence() {
char c;
scanf("%c", &c);
if (c != '\n') {
reverseSentence();
printf("%c", c);
}
}

15. Write a C Program to Make a Simple Calculator Using switch case.

Solution:-

#include 
int main() {
char operator;
double first, second;
printf("Enter an operator (+, -, *,): ");
scanf("%c", &operator);
printf("Enter two operands: ");
scanf("%lf %lf", &first, &second);

switch (operator) {
case '+':
printf("%.1lf + %.1lf = %.1lf", first, second, first + second);
break;
case '-':
printf("%.1lf - %.1lf = %.1lf", first, second, first - second);
break;
case '*':
printf("%.1lf * %.1lf = %.1lf", first, second, first * second);
break;
case '/':
printf("%.1lf / %.1lf = %.1lf", first, second, first / second);
break;
// operator doesn't match any case constant
default:
printf("Error! operator is not correct");
}

return 0;
}

OUTPUT
Enter an operator (+, -, *,): *
Enter two operands: 1.5
4.5
1.5 * 4.5 = 6.8

16. Write a code to generate random numbers in C Language.

Solution:- Random numbers in C Language can be generated as follows: 
#include&lt;stdio.h&gt;
#include&lt;stdlib.h&gt;
int main()
{
int a,b;
for(a=1;a&lt;=10;a++)
{
b=rand();
printf("%dn",b);
}
return 0;
}
Output : 
1987384758
2057844389
3475398489
2247357398
1435983905

17. Write a C program to print hello world without using a semicolon (;).

Solution:- 
#include&lt;stdio.h&gt;
void main()
{
if(printf("hello world")){}
}
Output: 
hello world

18. Write a program to swap two numbers without using the third variable.

Solution:- 
#include&lt;stdio.h&gt;
#include&lt;conio.h&gt;
main()
{
int a=10, b=20;
clrscr();
printf("Before swapping a=%d b=%d",a,b);
a=a+b;
b=a-b;
a=a-b;
printf("nAfter swapping a=%d b=%d",a,b);
getch();
}
Output : 
Before swapping a=10 b=20
After swapping a=20 b=10

19. Write a code to print the following pattern.

1 12 123 1234 12345

Solution:- 
#include<stdio.h>
int main()
{
      for(i=1;i<=5;1++)
      {
           for(j=1;j<=5;j++)
           {
                print("%d",j);
           }
           printf("n");
      }
      return 0;
}
 

20. How can you remove duplicates in an array?

Solution:- 
#include &lt;stdio.h&gt;
int main()
{
int n, a[100], b[100], calc = 0, i, j,count;
printf("Enter no. of elements in array.n");
scanf("%d", &amp;n);
printf("Enter %d integersn", n);
for (i = 0; i &lt; n; i++)
scanf("%d", &amp;a[i]);
for (i = 0; i&lt;n; i++)
{
for (j = 0; j&lt;calc; j++)
{
if(a[i] == b[j])
break;
}
if (j== calc)
{
b[count] = a[i];
calc++;
}
}
printf("Array obtained after removing duplicate elementsn");
for (i = 0; i&lt;calc; i++)
{
printf("%dn", b[i]);
}
return 0;
}
Output : 
Enter no. of elements in array. 5
Enter 5 integers
12
11
11
10
4
Array obtained after removing duplicate elements
12
11
10
4