Expression must have integral or unscoped enum type pow() func

Question

Im programming in c VS 2013

im trying to multiplicate the a[i] num by 10 raised by (max -1 -i). when max is the size of array, and i is initialed for (max -1). im using a for loop, i--.

im using the pow() function, and therefor had to define i as a float, or a double. Maybe max too, but it doesnt give me an error.

int sum = 0;
float j = 0, i;
int max;

printf("Enter number of digits: ");
scanf_s("%d", &max);

int *a;
a = (int *)malloc(max * sizeof(* a));

for (i = 0; i < max; i++)
{
    printf("\nEnter the %d digt: ", i + 1);
1   scanf_s("%d", &a[i]);
}

for (i = max - 1; i >= 0 ; i--)
{
2   sum = sum + a[i]*pow(10, max -1 -i);
    j++;
}

When trying to compile, it gives me an error at lines 1 and 2.. pointing on [i] and saying that expression must have integral or unscoped enum type

the (max - 1 -i) b.t.w is instead of an extra variable.. im trying to minimize them

help?

[Don't cast the result of malloc in C](http://stackoverflow.com/q/605845/995714) — phuclv, Sep 08 '15 at 06:09
@n.m. i do have, bc the pow() func demands one of its operators to be so — Daniel, Sep 08 '15 at 17:54
@daniel malloc() and its Family's return type are void*. In C you do not cast malloc. — Michi, Sep 08 '15 at 18:04
@Michi i guess im not familiar with the meaning of cast in the comput science.. bc i dont understand where i did it — Daniel, Sep 08 '15 at 19:07
If you didn't already read this, read it ==>> http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc — Michi, Sep 08 '15 at 19:09
Did you click on the link? There is an online compiler in there. You can enter code and it will compile and run it. I copied your code and added a few necessary things and made a few changes and it was compiled and executed and worked. Do you have a question about how this system works? — n. m. could be an AI, Sep 08 '15 at 23:04
"when not casting, it gives an error". That's because you are using a C++ compiler, not a C compiler. C++ and C are two different languages. — n. m. could be an AI, Sep 08 '15 at 23:08

score 3 · Answer 1 · answered Sep 08 '15 at 02:29

3

Exactly as the error message says. i must have an integral type such as int. You can't use a float as an array index.

answered Sep 08 '15 at 02:29

John Kugelman

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ok. so how can i solve this problem as described?.. regards to the pow() – Daniel Sep 08 '15 at 17:55
i meant, how can i use the pow() func without giving him j.. but giving him (max - 1 - i) – Daniel Sep 08 '15 at 19:20
I don't understand your question. You're already doing it with `pow(10, max -1 -i)`. Is there something wrong with that? – John Kugelman Sep 08 '15 at 19:28
Quit being rude. That call is fine. `int`s are automatically promoted to `float` or `double` as needed. Do you have `#include ` at the top of your source file? – John Kugelman Sep 08 '15 at 21:49
for sure.. otherwise i couldnt even use that function.. any way, i cant run the prog like this.. gives an error.. did u check it urself? – Daniel Sep 08 '15 at 22:08
Check [the link @n.m. posted](http://ideone.com/ztVbFi). That shows the program working. – John Kugelman Sep 08 '15 at 23:31
1

Also **what error does it give?** Stop asking us what we're seeing, or telling us to go check our error menu, whatever that is. **Tell us what you're getting**, because we're not getting what you're getting. – John Kugelman Sep 08 '15 at 23:34

score 2 · Answer 2 · answered Sep 08 '15 at 05:15

[too long for a comment]

If you have (more or less) complex expression in one line which does not compile, distrubute it over several lines to give the compiler a chance to point you what it does not like:

For example replace

sum = sum + a[i]*pow(10, max -1 -i);

by

sum = 
  sum + 
    a[i] * 
      pow(
        10, 
        max 
          -1 
          -i);

After have fixed the bug, remove those masive new-lines.

Expression must have integral or unscoped enum type pow() func

2 Answers2