# C Programming - Algorithm: Exercises, Practice, Solution

## C Programming Practice [28 exercises with solution]

[*An editor is available at the bottom of the page to write and execute the scripts.*]

**1.** Write a C program to get the indices of the two numbers of a given array of integers, such that the sum of the two numbers equal to a specific target. Go to the editor

*Expected Output*:

Original Array: 4 2 1 5 Target Value: 7 Indices of the two numbers whose sum equal to target value: 7 1 3

**2.** Write a C program to find length of the longest substring of a given string without repeating characters. Go to the editor

*Expected Output*:

Original String: xyzxyzyy Length of the longest substring without repeating characters: 3

**3.** Write a C program to find the median of the two given sorted arrays which are not empty. Go to the editor

*Expected Output*:

Median of the above two sorted arrays is: 10.000000

**4.** Write a C program to find the longest palindromic substring of a given string. Maximum length of the given string is 1000. Go to the editor

*Expected Output*:

Original String: yxypxst Longest palindromic substring of the said string: yxy

**5.** Write a C program to reverse digits of a given a 32-bit signed integer. Go to the editor

*Expected Output*:

Original integer: 123 Reverse integer : 321

**6.** Write a C program to convert a given integer to roman number. Go to the editor

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000

*Expected Output*:

Original integer: 12 Roman number of the said integer: XII

**7.** Write a C program to Write a C programming to convert a given roman number to an integer. Go to the editor

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000

*Expected Output*:

Original Roman number: XIV Roman to integer: 14

**8.** Write a C program to find all unique triplets in a given array integers whose sum equal to zero. Go to the editor

*Expected Output*:

Original Array: -2 0 0 1 1 Unique triplets of the said array whose sum equal to zero: -2 1 1

**9.** Write a C program to find all unique quadruplets in a given array of integers whose sum equal to zero. Go to the editor

*Expected Output*:

Original Array: 0 4 7 0 1 6 6 -3 Unique quadruplets of the said array whose sum equal to 12: 0 0 6 6 0 1 4 7

**10.** Write a C program to check if a given string is valid or not, the string contains the characters '(', ')', '{', '}', '[' and ']'. The string is valid if the open brackets must be closed by the same type of brackets and in correct order.Go to the editor

*Expected Output*:

false

**11.** Write a C program to generate all combinations of well-formed parentheses from n given pairs of parentheses.Go to the editor

Example: Input n = 5 Output: (()())(()) (()())()() (())((())) ..... (())(())() (())()(()) (())()()()

*Expected Output*:

((((())))) (((()()))) (((())())) (((()))()) (((())))() ((()(()))) ((()()())) ((()())()) ((()()))() ((())(())) ((())()()) ((())())() ((()))(()) ((()))()() (()((()))) (()(()())) (()(())()) (()(()))() (()()(())) (()()()()) (()()())() (()())(()) (()())()() (())((())) (())(()()) (())(())() (())()(()) (())()()() ()(((()))) ()((()())) ()((())()) ()((()))() ()(()(())) ()(()()()) ()(()())() ()(())(()) ()(())()() ()()((())) ()()(()()) ()()(())() ()()()(()) ()()()()()

**12.** Write a C program to remove the duplicates from a given array of integers. Go to the editor

*Expected Output*:

Original array: 1 1 2 3 4 4 5 6 6 6 After removing duplicates from the above sorted array: 1 2 3 4 5 6

**13.** Write a C program to remove all instances of a given value in a given array of integers and return the length of the new array. Go to the editor

*Expected Output*:

Original array: 1 1 2 3 4 4 5 6 6 6 Size of the new array after removing the value 4: 8

**14.** Write a C program to find the index of the first occurrence of a given string within another given string. If not found return -1. Go to the editor

*Expected Output*:

Main string: w3resource.com Substring searched in main string: source Starting position of the substring in the main string: 4

**15.** Write a C program to divide two given integers without using multiplication, division and mod operator. Return the quotient after dividing. Go to the editor

*Expected Output*:

Quotient after dividing 15 and 3 : 5

**16.** Write a C program to find the length of the longest valid (correct-formed) parentheses substring of a given string. Go to the editor

*Expected Output*:

Original Parentheses string: (()))

Length of longest parentheses: 4

**17.** The natural numbers below 10 that are multiples of 3 or 7 are 3, 7, 6 and 9. The sum of these multiples is 25.

Write a C programming to find the sum of all the multiples of 3 or 7 below 100. Go to the editor

*Expected Output*:

2208

**18.** In mathematics, the Fibonacci numbers, commonly denoted F_{n} form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is, and for n > 1. By starting with 1 and 2, the first 10 terms will be:
1, 2, 3, 5, 8, 13, 21, 34, 55, 89, . . .

Write a C programming to find the sum of the even-valued terms from the terms in the Fibonacci sequence whose values do not exceed one million. Go to the editor

*Expected Output*:

10

**19.** The prime factors of 13195 are 5, 7, 13, 29.

Write a C programming to find the largest prime factor of the number 438927456?. Go to the editor

*Expected Output*:

415651

**20.** A palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward, such as taco cat or madam or racecar or the number 10801. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Write a C programming to find the largest palindrome made from the product of two 3-digit numbers. Go to the editor

*Expected Output*:

906609

**21.** 2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.

Write a C programming to find the smallest positive number that is evenly divisible by all of the numbers from 1 to 20? Go to the editor

*Expected Output*:

232792560

**22.** The sum of the squares of the first ten natural numbers is,

1^{2} + 2^{2} + ... + 10^{2} = 385

The square of the sum of the first ten natural numbers is,

(1 + 2 + ... + 10)^{2} = 55^{2} = 3025

Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 − 385 = 2640.

Write a C programming to find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum. Go to the editor

*Expected Output*:

25164150

**23.** By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.

The first six prime numbers are 2, 3, 5, 7, 11, and 13.

Write a C programming to get the 1001st prime number? Go to the editor

*Expected Output*:

7927

**24.** The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

73167176531330624919225119674426574742355349194934

96983520312774506326239578318016984801869478851843

85861560789112949495459501737958331952853208805511

12540698747158523863050715693290963295227443043557

66896648950445244523161731856403098711121722383113

62229893423380308135336276614282806444486645238749

30358907296290491560440772390713810515859307960866

70172427121883998797908792274921901699720888093776

65727333001053367881220235421809751254540594752243

52584907711670556013604839586446706324415722155397

53697817977846174064955149290862569321978468622482

83972241375657056057490261407972968652414535100474

82166370484403199890008895243450658541227588666881

16427171479924442928230863465674813919123162824586

17866458359124566529476545682848912883142607690042

24219022671055626321111109370544217506941658960408

07198403850962455444362981230987879927244284909188

84580156166097919133875499200524063689912560717606

05886116467109405077541002256983155200055935729725

71636269561882670428252483600823257530420752963450.

Write a C programming to find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product? Go to the editor

*Expected Output*:

40824

**25.** A Pythagorean triplet is a set of three natural numbers, x < y < z, for which,

x^{2} + y^{2} = z^{2}

For example, 3^{2} + 4^{2} = 9 + 16 = 25 = 5^{2}.

There exists exactly one Pythagorean triplet for which x +y + z = 1000.

Write a C programming to find the product xyz. Go to the editor

*Expected Output*:

Numbers are: 200, 375, 425 Product of x, y, z is : 31875000

**26.** A prime number is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 6 is composite because it is the product of two numbers (2 × 3) that are both smaller than 6.

The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

Write a C programming to find the sum of all the primes below ten thousand. Go to the editor

*Expected Output*:

5736396

**27.** In the 20×20 grid below, four numbers along a diagonal line have been marked in red.

08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08

49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00

81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65

52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91

22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80

24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50

32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70

67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21

24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72

21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95

78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92

16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57

86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58

19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40

04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66

88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69

04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36

20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16

20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54

01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48

The product of these numbers is 26 × 63 × 78 × 14 = 1788696.

Write a C programming to find the greatest product of four adjacent numbers in the same direction (up, down, left, right, or diagonally) in the 20×20 grid. Go to the editor

*Expected Output*:

70600674

**28.** Write a C programming to find the first missing positive integer from a given unsorted integer array. Go to the editor

*Expected Output*:

2

## C Programming Code Editor:

**More to Come !**

**Do not submit any solution of the above exercises at here, if you want to contribute go to the appropriate exercise page.**

## C Programming: Tips of the Day

**Setting variable to NULL after free:**

Setting unused pointers to NULL is a defensive style, protecting against dangling pointer bugs. If a dangling pointer is accessed after it is freed, you may read or overwrite random memory. If a null pointer is accessed, you get an immediate crash on most systems, telling you right away what the error is.

For local variables, it may be a little bit pointless if it is "obvious" that the pointer isn't accessed anymore after being freed, so this style is more appropriate for member data and global variables. Even for local variables, it may be a good approach if the function continues after the memory is released.

To complete the style, you should also initialize pointers to NULL before they get assigned a true pointer value.

Ref : https://bit.ly/3pe0XYk

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