Write a function template to perform linear search in an array in C++ program.

  here's an example program in C++ that uses a function template to perform linear search on an array:

#include <iostream>

using namespace std;

template <typename T>
int linearSearch(T arr[], int size, T key) {
    for (int i = 0; i < size; i++) {
        if (arr[i] == key) {
            return i; // Return the index where key was found
        }
    }
    return -1; // Key not found in array
}

int main() {
    int intArr[] = { 1, 2, 3, 4, 5 };
    int intSize = sizeof(intArr) / sizeof(intArr[0]);
    int intKey = 3;

    cout << "Index of " << intKey << " in intArr: " << linearSearch(intArr, intSize, intKey) << endl;

    double doubleArr[] = { 1.2, 2.3, 3.4, 4.5, 5.6 };
    int doubleSize = sizeof(doubleArr) / sizeof(doubleArr[0]);
    double doubleKey = 4.5;

    cout << "Index of " << doubleKey << " in doubleArr: " << linearSearch(doubleArr, doubleSize, doubleKey) << endl;
    return 0;
}

Output:

Index of 3 in intArr: 2
Index of 4.5 in doubleArr: 3

In this program, the linearSearch function template takes three arguments: arr is the array to be searched, size is the size of the array, and key is the value being searched for. The function loops through each element of the array, comparing it with the key value. If a match is found, the function returns the index of the matching element. If no match is found, the function returns -1.

In the main function, two arrays are declared: one of int type and one of double type. The sizeof operator is used to calculate the size of each array. A key value is also declared for each array. The linearSearch function is called twice with different types of arrays and keys. The returned index value (or -1 if key not found) is printed to the console using cout.