this is my code I want to try to compare my array with the number but I give me some error basically, I am trying to find a number with a linear search and print the index of that number in c

   // linear search 
    #include <iostream>
    using namespace std;
    
    int search(int arr, int n, int x)
    {
        int i=0;
        for (i = 0; i < n; i  ){
            if (arr[i] == x){
                return i;}
        }
        return -1;
    }
    
    // Driver code
    int main(void)
    {
        int size;
        int temp;
        cout << "Enter Size of Arry";
        cin >> size;
        int  arr[size];
        for(int i=0;i<size;i  ){
            cout << "Enter a " << i << "Element of your arry : ";
            cin >> temp;
            arr[i]=temp;
    
        }
        
    
         cout << "Enter the number that you will find index";
            int x;
         cin >> x;
        // Function call
        int result = search(arr, size, x);
        (result == -1)
            ? cout << "Element is not present in array"
            : cout << "Element is present at index " << result;
        return 0;
    }

this is the error

PS C:\Users\talha\OneDrive\Desktop\Study_Material\DSA_lab\cs201149_lab1_3C> g   Q1.cpp -o Q11.exe
Q1.cpp: In function 'int search(int, int, int)':
Q1.cpp:9:12: error: invalid types 'int[int]' for array subscript
   if (arr[i] == x){
            ^
Q1.cpp: In function 'int main()':
Q1.cpp:35:34: error: invalid conversion from 'int*' to 'int' [-fpermissive]
  int result = search(arr, size, x);
                                  ^
Q1.cpp:5:5: note:   initializing argument 1 of 'int search(int, int, int)'
 int search(int arr, int n, int x)
     ^~~~~~
PS C:\Users\talha\OneDrive\Desktop\Study_Material\DSA_lab\cs201149_lab1_3C> 

CodePudding user response：

First in C , the size of an array must be a compile-time constant.So, take for example the following code snippets:

int n = 10;
int arr[n]; //INCORRECT because n is not a constant expression

The correct way to write the above would be:

const int n = 10;
int arr[n]; //CORRECT

Similarly, the following(which you did in your code example) is incorrect:

    int size;
    int temp;
    cout << "Enter Size of Arry";
    cin >> size;
    int  arr[size];//INCORRECT because variable size is not a constant  expression

You should use std::vector for your purpose as shown below:

#include <iostream>
#include <vector>
using namespace std;
//the first argument is a vector<int>
int search(std::vector<int> arr, int x)
{
    int i=0;
    for (i = 0; i < arr.size(); i  ){//use size()member function
        if (arr[i] == x){
            return i;}
    }
    return -1;
}

// Driver code
int main(void)
{
    int size;
    int temp;
    cout << "Enter Size of Arry";
    cin >> size;
    //create a vector instead of an array 
    std::vector<int> arr(size);
    for(int i=0;i<arr.size();i  ){//use the size member function
        cout << "Enter a " << i << "Element of your arry : ";
        cin >> temp;
        arr[i]=temp;

    }
    

     cout << "Enter the number that you will find index";
        int x;
     cin >> x;
    // Function call
    int result = search(arr,  x);//no need to pass the size of the vector
    (result == -1)
        ? cout << "Element is not present in array"
        : cout << "Element is present at index " << result;
    return 0;
}

Note that you can also use std::find instead of writing your own search algorithm.

CodePudding user response：

For starters variable length arrays like this

int  arr[size];

is not a standard C feature. Instead it would be much better to use the standard container std::vector<int> in a C program.

Secondly the function declaration is incorrect. The first parameter is declared as having the type int.

int search(int arr, int n, int x)

You need to declare the function the following way

int search(int arr[], int n, int x)

or equivalently

int search(int *arr, int n, int x)

Pay attention to that there is standard algorithm std::find in C that performs searching an element in a container.