C++ | Comparing two arrays using std::mismatch (or another STL alternative)

Question

I am faced with the task of comparing two c++ arrays that are of int data type. I specifically cannot use any loops (for, while) of my own, and was encouraged to use an STL function. I found std::mismatch() and it seems to be what I want, but I am unable to get it working with a basic array.

Here is my code:

#include <iostream>     // cout
#include <algorithm>    // std::mismatch
#include <utility>      // pair

int main()
{
    int a[10] = {1,3,5,7,9,11,13,15,17,19};
    int b[10] = {2,4,6,8,10,12,14,16,18,20};

    std::pair<int, int> result = 
        std::mismatch(a, a + 9, b);
    
    std::cout<<result.first<<" "<<result.second<<std::endl;

    return 0;
}

I am getting the following error:

error: conversion from 'std::pair' to non-scalar type 'std::pair' requested

I am pretty new to C++, so I don't really know what this means.

Answer 1

std::mismatch returns a pair of iterators to the container, not a pair of ints. In this case, since you have an array, the iterator type is int*.

The simple solution is to deduce the type when calling it instead:

auto result = std::mismatch(a, a + 9, b);

From c++17, you can name the individual elements of the pair as well:

auto [i, j] = std::mismatch(a, a + 9, b);