Can I have different types in the init-expression of a for loop?

Question

The following code will not compile:

#include <iostream>

int main(){

    for (int i = 0, double j = 0; i < 10; ++i, j+=.1){
        std::cout << i << " " << j << '\n';
    }

    return 0;
}

Is it possible to initialize two different types, or do I need to create a struct/pair/etc?

Is it necessary that the scope be limited to the loop? Would it be an acceptable alternative to just put gratuitous braces around the `for` loop? — Brian Cain, Apr 03 '13 at 18:29
possible dup http://stackoverflow.com/questions/2687392/is-it-possible-to-declare-two-variables-of-different-types-in-a-for-loop — Shafik Yaghmour, Apr 03 '13 at 18:29

score 9 · Accepted Answer · answered Apr 03 '13 at 18:30

9

No.

But you can define an anonymous struct right there as:

for (struct { int i; double j; } x = {0,0};  x.i < 10; ++x.i, x.j+=.1)
{
    std::cout << x.i << " " << x.j << '\n';
}

See the initialization part:

struct { int i; double j; } x = {0,0};

It defines an anonymous struct, then creates an object x and initializes it with {0,0} which initializes both members i and j with 0.

answered Apr 03 '13 at 18:30

Nawaz

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It does not compile for me on VC++ :O, does it for you? – Saqlain Apr 03 '13 at 18:36
@Saqlain: Yes. [See yourself here](http://coliru.stacked-crooked.com/view?id=6bd36fc4b91846b1084d84207525b5a3-61c3814520a8d4318f681038dc4b4da7). – Nawaz Apr 03 '13 at 18:38
1

http://stackoverflow.com/a/889001/34509 – Johannes Schaub - litb Apr 03 '13 at 18:40
On VS 2005 i get below error with above code error C2332: 'struct' : missing tag name error C2143: syntax error : missing ')' before '{' warning C4094: untagged 'struct' declared no symbols error C2059: syntax error : 'empty declaration' error C2143: syntax error : missing ';' before ')' error C2143: syntax error : missing ';' before ')' error C2065: 'x' : undeclared identifier error C2059: syntax error : '{' error C2143: syntax error : missing ';' before '{' error C2143: syntax error : missing ';' before '}' – Saqlain Apr 03 '13 at 18:42
@Saqlain: That means MSVC2005 has bug. – Nawaz Apr 03 '13 at 18:42
Yep, that can be true! – Saqlain Apr 03 '13 at 18:43

score 2 · Answer 2 · answered Apr 03 '13 at 18:30

Not possible, but there is way:

double var1;
int var2;
for (var2 = 0,var1 = 0.0; var2 < 12; var2++){}

If you want to limit scope of f and i then enclose them in {}, just like

{
    double var1;
    int var2;
    for (var2 = 0,var1 = 0.0; var2 < 12; var2++){}
}

score 1 · Answer 3 · answered Apr 03 '13 at 18:29

1

No, you can't. You can have multiple variables, but they have to be the same type.

answered Apr 03 '13 at 18:29

Luchian Grigore

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score 0 · Answer 4 · answered Apr 03 '13 at 18:30

0

They have to be the same type, but you can use structs to bypass that.

for (struct {int j; char i;} loop = {0, 'e'}; loop.i < 33; ++loop.j, ++loop.i)
{
    std::cout << loop.i << '\n';
}

answered Apr 03 '13 at 18:30

frickskit

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score 0 · Answer 5 · answered Apr 03 '13 at 18:34

0

Can do the following

#include<cstdlib>
#include<iostream>

int main(int argc, char *argv[]){

    int i; double j;
    for(i = 0, j = 0; i < 10; ++i, j+= .1){
        std::cout << i << " " << j << '\n';
    }


    return EXIT_SUCCESS;
}

answered Apr 03 '13 at 18:34

Mushy

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Can I have different types in the init-expression of a for loop?

5 Answers5