C++ Primer 3.3.3

Reply to C++ Primer 3.3.3 on Sat, 01 Mar 2014 12:32:59 GMT

hihohohi — Sat, 01 Mar 2014 12:32:59 GMT

Hey, this is my program:

std::vector test(5);
    int a, b, c, d, s;
    std::cin >> a >> b >> c >> d;
    test.push_back(a);
    test.push_back(b);
    test.push_back(c);
    test.push_back(d);
    s = test[0] + test [1];
    std::cout << s << std::endl;
    s = test[2] + test [3];
    std::cout << s << std::endl;
    s = test[4] + test [5];
    std::cout << s << std::endl;
    s = test[0] + test [5];
    std::cout << s << std::endl;

it shall print the sum of the pairs and the sum of the first and last number in 'test'. I did write and read stuff this way already with strings, but now when i use ints, it doesn't work ...

if i input '1 2 3 4' the output is '0 0 1 1'
if i input '1 1 1 1' its the same.

please help me,
thanks.

Benno

Reply to C++ Primer 3.3.3 on Sat, 01 Mar 2014 12:41:20 GMT

volkard — Sat, 01 Mar 2014 12:41:20 GMT

hihohohi schrieb:

Hey, this is my program:
std::vector test(5);
    int a, b, c, d, s;
    std::cin >> a >> b >> c >> d;
    test.push_back(a);
    test.push_back(b);
    test.push_back(c);
    test.push_back(d);
    s = test[0] + test [1];
    std::cout << s << std::endl;
    s = test[2] + test [3];
    std::cout << s << std::endl;
    s = test[4] + test [5];
    std::cout << s << std::endl;
    s = test[0] + test [5];
    std::cout << s << std::endl;
it shall print the sum of the pairs and the sum of the first and last number in 'test'. I did write and read stuff this way already with strings, but now when i use ints, it doesn't work ...

if i input '1 2 3 4' the output is '0 0 1 1'
if i input '1 1 1 1' its the same.

please help me,
thanks.

Benno

sum of pairs:

s = test[0] + test [1];
    std::cout << s << std::endl;
    s = test[1] + test [2];
    std::cout << s << std::endl;
    s = test[2] + test [3];
    std::cout << s << std::endl;

so you dont need s[5].

std::vector test;//not initiallly fillng with 5 zeros

Reply to C++ Primer 3.3.3 on Sat, 01 Mar 2014 12:48:56 GMT

hihohohi — Sat, 01 Mar 2014 12:48:56 GMT

oh ya the pushback function adds to the end
thanks man, works now.

std::vector test;
    int a, b, c, d, e, s;
    std::cin >> a >> b >> c >> d;
    test.push_back(a);
    test.push_back(b);
    test.push_back(c);
    test.push_back(d);
    test.push_back(e);
    s = test[0] + test [1];
    std::cout << s << std::endl;
    s = test[2] + test [3];
    std::cout << s << std::endl;
    s = test[0] + test [3];
    std::cout << s << std::endl;

Reply to C++ Primer 3.3.3 on Sat, 01 Mar 2014 12:52:41 GMT

Skym0sh0 — Sat, 01 Mar 2014 12:52:41 GMT

If you want to optimize try using std::vector::reserve. It allocates memory for n elements, but the size stays at the old value (in this case 0), so push_back will result in the way you need it.

But in this special case it might be no optimization due to too less values. Long story short, you wont need it

Reply to C++ Primer 3.3.3 on Sat, 01 Mar 2014 12:58:10 GMT

hihohohi — Sat, 01 Mar 2014 12:58:10 GMT

Skym0sh0 schrieb:

If you want to optimize try using std::vector::reserve. It allocates memory for n elements, but the size stays at the old value (in this case 0), so push_back will result in the way you need it.

But in this special case it might be no optimization due to too less values. Long story short, you wont need it

i will keep that in mind for later tasks
thanks