CODEWITHSUNDEEP
cfor-loopsyntax-error
kber
kber

Reputation: 19

Syntax error with multiple declarations in for loop

#include <stdio.h>
#include <math.h>
#include <conio.h>
#include <locale.h>

int main()
{
    setlocale(LC_ALL, "Rus");

    float arr[25];
    int i;
    double x;
    int a, b, c, e, f;
    double y = a * pow(x, 2) + b * x + c;

    printf("a: ");
    scanf_s("%d", &a);

    printf("b: ");
    scanf_s("%d", &b);

    printf("c: ");
    scanf_s("%d", &c);

    printf("e: ");
    scanf_s("%d", &e);

    printf("f: ");
    scanf_s("%d", &f);

    double interval = (f - e) / 25.0 ;

    for (int i = 0, double x = e; i < 25; i++, x += interval)
    {
        printf("%f", y);
        x++;
    }

    system("pause");
}

I get [Error] expected identifier or '(' before 'double'. How can i fix it? It doesnt seem like i really need to change something in 

for (int i = 0, double x = e; i < 25; i++, x += interval)

or maybe im wrong and dont know how to write multiple conditions.

Upvotes: 0

Views: 629

Answers (4)

Jose
Jose

Reputation: 3460

You could embedded them into a struct. I do not recommend it because IMO it is not a good coding practice as it is not easy to understand (at first sight)…

typedef struct {int i; double x;} S;
for (S yourStruct = {0,e}; yourStruct.i < 25 ; yourStruct.i++, yourStruct.x += interval)
{
    printf("%f", y);
    yourStruct.x++;
}

Upvotes: 1

melpomene
melpomene

Reputation: 85757

Yeah, you can't do that.

By the way, those are declarations, not conditions. Only the middle part of a for loop is a condition.

You can declare multiple variables in the first part of a for loop, but only if they have the same base type (e.g. int):

for (int x = 1, y = 2, z = 3; ...; ...)

The workaround in your case is to declare at least one of the variables outside of the loop:

{  // this outer block limits the scope of x
    double x = e;
    for (int i = 0; i < 25; i++, x += interval) 
    {
        printf("%f", y);
        x++;
    }
}

That said, your code doesn't really make sense. Your loop doesn't use x, so there's no point in setting it. On the other hand, the value you're printing 25 times (y) doesn't change in the loop. It's set at the top of your main function, computed from a different x variable that is uninitialized.

You should move the declaration and initialization of y into the loop and delete the outer x. See also https://stackoverflow.com/a/53238897/1848654.

Upvotes: 2

Aconcagua
Aconcagua

Reputation: 25518

It is not really a matter of the for loop:

void f(void)
{
    int x, y; // legal - and you can do the same in a for loop's initialization section
    int z, double d; // can't do that either, even outside for loop...
};

All variables that you declare in a single expression need to have the same (base!) type, be it within for loop, function body or global. 'Base type': Well, because you legally can do stuff like int x, *p;, with x and p being of different type, but base/underlying type in both cases is int.

Upvotes: 0

perreal
perreal

Reputation: 97918

You can't define variables with multiple types with the comma:

for(int i = 0, double x...

Instead:

x = e;
for (int i = 0; i<...

and the x is already defined above.

Upvotes: 1

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