# C Exercises: Find the missing number from a given array

## C Array: Exercise-36 with Solution

Write a program in C to find the missing number in a given array. There are no duplicates in the list.

**Visual Presentation:**

**Sample Solution:**

**C Code:**

```
#include <stdio.h>
// Function to find the missing number in an array
int pickMissNumber(int *arr1, int ar_size) {
int i, sum = 0, n = ar_size + 1;
// Calculating the sum of all elements in the array
for (i = 0; i < ar_size; i++) {
sum = sum + arr1[i];
}
// Calculating the missing number using the sum of the first 'n' natural numbers formula
return (n * (n + 1)) / 2 - sum;
}
// Main function
int main() {
int i;
int arr1[] = {1, 3, 4, 2, 5, 6, 9, 8};
int ctr = sizeof(arr1) / sizeof(arr1[0]);
// Displaying the given array
printf("The given array is : ");
for (i = 0; i < ctr; i++) {
printf("%d ", arr1[i]);
}
printf("\n");
// Finding and displaying the missing number
printf("The missing number is : %d \n", pickMissNumber(arr1, ctr));
return 0;
}
```

Sample Output:

The given array is : 1 3 4 2 5 6 9 8 The missing number is : 7

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