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C program to find the missing number in the array

Here, we are going to learn how to find the missing number in the array in C programming language?
Submitted by Nidhi, on July 11, 2021

Problem statement

Here, we will create an array of integers then we will find the missing number from the array.

Finding the missing number in the array

The source code to find the missing number in the array is given below. The given program is compiled and executed using GCC compile on UBUNTU 18.04 OS successfully.

// C program to find the missing number in the array

#include <stdio.h>

int main()
{
    int arr[] = { 1, 2, 3, 5, 6 };

    int size = 0;
    int i = 0;
    int missing = 0;

    size = sizeof(arr) / sizeof(arr[0]);

    missing = (size + 1) * (size + 2) / 2;

    for (i = 0; i < size; i++)
        missing = missing - arr[i];

    printf("Missing number is: %d\n", missing);

    return 0;
}

Output

Missing number is: 4

Explanation

Here, we created an array arr with 5 elements. And, we also created three variables size, missing, i that are initialized with 0. Then we found missing elements from the array and printed the result on the console screen.

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