Easiest Solution in C
Code
# Code
```c []

char* sortVowels(char* s) {
    bool isVowel(char ch) {
        return ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U' ||
               ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u';
    }
    
    int comp(const void* a, const void* b) { return (*(char*)a - *(char*)b); }

    int len = strlen(s);
    char* arr = malloc(len * sizeof(char));
    int ind = 0;
    for (int i = 0; i < len; i++) {
        if (isVowel(s[i])) {
            arr[ind++] = s[i];
        }
    }
    qsort(arr, ind, sizeof(char), comp);

    ind = 0;
    for (int i = 0; i < len; i++) {
        if (isVowel(s[i])) {
            s[i] = arr[ind++];
        }
    }
    return s;
}
```
['String', 'C', 'Sorting']