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c++arraysvisual-studioif-statement
The Riser
The Riser

Reputation: 329

Array value as a condition

I have an array of integers called test containing 7 elements,I want to write an if statement to check if the 6 first values of the array are equal to a certain collection of values,what I tried was:

if (test == {1, 0, 1, 0, 0, 0} ) {
//statement(s)
}

However,the line containing the condition gives me an "expected an expression error",what am I doing wrong? Thanks in advance.

Upvotes: 0

Views: 171

Answers (3)

Ghazi
Ghazi

Reputation: 126

Here is a way to do it (if your test is an std::array):

#include <algorithm>

...

std::vector<int> v({1, 0, 1, 0, 0, 0});
if( (v.size()==test.size()) && std::equal(test.begin(), test.end(), v.begin()) ) {
// statement(s)
}

or

#include <algorithm>

...

std::vector<int> v({1, 0, 1, 0, 0, 0});
if( std::equal(test.begin(), test.end(), v.begin(), v.end()) ) {
// statement(s)
}

Upvotes: 0

Ted Lyngmo
Ted Lyngmo

Reputation: 117308

C++17 versions using deduction guides:

std::array

std::array test{1, 0, 1, 0, 0, 0};

if(test == std::array{1, 0, 1, 0, 0, 0}) {
    std::cout << "equal\n";
}

std::vector

std::vector test{1, 0, 1, 0, 0, 0};

if(test == std::vector{1, 0, 1, 0, 0, 0}) {
    std::cout << "equal\n";
}

Upvotes: 2

pptaszni
pptaszni

Reputation: 8228

If you use std::array you can simply rely on operator==

  std::array<int, 7> a1 = {1, 2, 3, 4, 5, 6, 7};
  std::array<int, 7> a2 = {2, 3, 4, 5, 6, 7, 8};
  std::cout << "a1 == a1 " << (a1 == a1) << std::endl;
  std::cout << "a1 == a2 " << (a1 == a2) << std::endl;

However, if for some reason you need to use C-style array, then you can use std::memcmp, which will compare the arrays byte by byte:

  int ca1[7] = {1, 2, 3, 4, 5, 6, 7};
  int ca2[7] = {2, 3, 4, 5, 6, 7, 8};
  std::cout << "ca1 == ca1 " << (std::memcmp(ca1, ca1, sizeof(ca1)) == 0) << std::endl;
  std::cout << "ca1 == ca2 " << (std::memcmp(ca1, ca2, sizeof(ca1)) == 0) << std::endl;

Note that you need to compare the std::memcmpy result with 0, which means that they are equal. reference However, in this approach you should first check if the dimensions are equal.

Upvotes: 0

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