i can't use an array in other function? - c

Question

I'm writing a program to print a numbers in array then used function to split the array to an odd and even number. I've done this part, then I have to sent each of the odd and even array to another function that calculate the largest number in each array and return the calculated value. It seem there something missing in the main function.
#include <stdio.h>
void split();
int largest(int arr[]);
int main() {
int a[11] = {2, 4, 5, 6, 7, 1, 8, 3, 9, 14, 17};
printf("the values of the array is :\n");
for (int i = 0; i < 11; i++) {
printf("%d ", a[i]);
}
split();
int z = largest(odd);
printf("the max value in odd array is :%d\n", z);
}
void split() {
int i, evenNumber = 0, oddNumber = 0;
int even[11], odd[11];
int a[11] = {2, 4, 5, 6, 7, 1, 8, 3, 9, 14, 17};
for (i = 0; i < 11; i++) {
if (a[i] % 2 == 0) {
even[evenNumber++] = a[i];
} else {
odd[oddNumber++] = a[i];
}
}
printf("\nEven :\n");
for (i = 0; i < evenNumber; i++) {
printf("%d ", even[i]);
}
printf("\nOdd :\n");
for (i = 0; i < oddNumber; i++) {
printf("%d ", odd[i]);
}
}
int largest(int odd[]) {
int max;
max = odd[0];
for (int i = 0; i < 11; i++) {
if (max < odd[i]) {
max = odd[i];
}
}
return max;
}

Answer 1

You actually can use arrays in other functions. However, the problem you are running into is scope.
The Problem
In your main function,
int main ()
{
int a[11] = {2,4,5,6,7,1,8,3,9,14,17};
printf("the values of the array is :\n");
for (int i = 0 ; i<11 ; i++){
printf("%d ",a[i]);
}
split();
int z = largest(odd);
printf("the max value in odd array is :%d\n",z);
}
the line int z = largest(odd); uses the variable odd. However, odd is never defined in main. Rather, odd is defined in the scope of split().
It appears you think that because you are calling split() in main, that somehow you will able to access odd in main after you call split(). This is not true. Even though odd is defined in split(), it is defined only in split(). So even though main calls split(), odd is still not defined in main.
This is because a variable is limited to the scope in which it is defined. If a variable is defined in a function (i.e. the function is its scope), it is accessible only within that function, even if that function is used elsewhere. If you want to use a variable outside of the function in which it is defined, you must somehow "return" that variable from the function.
I strongly recommend reading a tutorial on how "scope" works in C, e.g. this tutorial.
The Solution
You have a two main options:
Rewrite split() to somehow return odd.
Move the contents of split() to main. I.e. don't make split() a separate function.
Unless you have a specific reason for keeping split() as a separate function, I would strongly recommend just moving its contents into main. Otherwise, you will have to pass multiple parameters as references to make split() work the way you want it to.
If we move the contents of split() into main (and make the necessary adjustments to remove duplicate variables), this is what the new code will look like:
#include <stdio.h>
int largest(int arr[]);
int main() {
int a[11] = { 2, 4, 5, 6, 7, 1, 8, 3, 9, 14, 17 };
printf("the values of the array is :\n");
for (int i = 0; i < 11; i++) {
printf("%d ", a[i]);
}
int evenNumber = 0, oddNumber = 0;
int even[11], odd[11];
for (int i = 0; i < 11; i++) {
if (a[i] % 2 == 0) {
even[evenNumber++] = a[i];
} else {
odd[oddNumber++] = a[i];
}
}
printf("\nEven :\n");
for (int i = 0; i < evenNumber; i++) {
printf("%d ", even[i]);
}
printf("\nOdd :\n");
for (int i = 0; i < oddNumber; i++) {
printf("%d ", odd[i]);
}
int z = largest(odd);
printf("the max value in odd array is :%d\n", z);
}
int largest(int odd[]) {
int max = odd[0];
for (int i = 0; i < 11; i++) {
if (max < odd[i]) {
max = odd[i];
}
}
return max;
}
One more comment:
Whenever you pass an array to a function, you should always pass the length of the array too. For example:
int largest(int odd[], int len) {
int max = odd[0];
for (int i = 0; i < len; i++) {
if (max < odd[i]) {
max = odd[i];
}
}
return max;
}
And then you would call largest(int[], int) like this:
largest(odd, 11);