# C Programming - Challenges: Exercises, Practice, Solution

## C Challenges [35 exercises with solution]

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**1.** Write a C program to get the indices of two numbers in a given array of integers. This will enable you to get the sum of two numbers equal to a specific target.

*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 the length of the longest substring of a given string without repeating characters.

*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. >

*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. >

*Expected Output*:

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

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

*Expected Output*:

Original integer: 123 Reverse integer : 321

**6.** Write a C program to convert a given integer to a Roman number. >

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 convert a Roman number to an integer. >

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 distinct triplets in a given array of integers whose sum is equal to zero. >

*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 distinct quadruplets in a given array of integers whose sum is equal to zero. >

*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 with the same type of bracket and in the correct order. >

*Expected Output*:

false

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

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

*Expected Output*:

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

**12.** Write a C program to remove duplicates from a given array of integers.. >

*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 from a given array of integers and return the length of the updated array. >

*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. >

*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 the multiplication, division and mod operator. Return the quotient after dividing. >

*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. >

*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 program to find the sum of all the multiples of 3 or 7 below 100. >

*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 program to find the sum of the even-valued terms from the terms in the Fibonacci sequence whose values do not exceed one million. >

*Expected Output*:

10

**19.** Write a C program to find the largest prime factor of the number 438927456. >

*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 program to find the largest palindrome made from the product of two 3-digit numbers. >

*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 program to find the smallest positive number that is evenly divisible by all of the numbers from 1 to 20? >

*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 program to find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum. >

*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 program to get the 1001st prime number? >

*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 program to find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

*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 program to find the product of xyz. >

*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 program to find the sum of all prime numbers below ten thousand. >

*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 program to find the greatest product of four adjacent numbers in the same direction (up, down, left, right, or diagonally) in the 20×20 grid. >

*Expected Output*:

70600674

**28.** Write a C program to find the first missing positive integer in a given unsorted integer array. >

*Expected Output*:

2

**29.** Write a C program to find the minimum number of characters that must be inserted into a given string with no whitespace characters to make it a palindrome. >

**Sample Input:** pps

Output: 1

**30.** Write a C program to create and display all prime numbers in strictly ascending decimal digit order. >

**Sample Data:** 2, 3, 5, 7, 13, 17, 19, 23, 29, 37, 47, 59, 67, 79,..

**31.** Write a C program to find the type of progression (arithmetic progression/geometric progression) and the next successive member of the three successive members of a sequence. >

**Sample Data:** 2, 6, 18, 54, ..

**32.** Write a C# Sharp program to create and display all prime numbers in strictly descending decimal digit order. >

**Sample Data:**

2, 3, 5, 7, 31, 41, 43, 53, 61, 71, 73, 83, 97, 421, 431.....

**33.** Write a C program to generate attractive numbers up to 100. >

**34.** Write a C program (subroutine, function, procedure, whatever it may be called in your language) to test if a number is a colorful number or not. >

**Sample Data:**

Colorful numbers less than 100:

0 1 2 3 4 5 6 7 8 9

23 24 25 26 27 28 29 32 34 35

36 37 38 39 42 43 45 46 47 48

49 52 53 54 56 57 58 59 62 63

64 65 67 68 69 72 73 74 75 76

78 79 82 83 84 85 86 87 89 92

93 94 95 96 97 98

**35.** Write a C program to generate a text calendar for any given year. >

**Sample Data:**

**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

**String literals: Where do they go?**

A common technique is for string literals to be put in "read-only-data" section which gets mapped into the process space as read-only (which is why you can't change it).

It does vary by platform. For example, simpler chip architectures may not support read-only memory segments so the data segment will be writable.

Rather than try to figure out a trick to make string literals changeable (it will be highly dependent on your platform and could change over time), just use arrays:

char foo[] = "...";

The compiler will arrange for the array to get initialized from the literal and you can modify the array.

Ref : https://bit.ly/3jNw4WX

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