How to get the most frequent letter in a word? - c

Question

I am trying to get the most frequent letter in a string with only uppercased letters and no spaces between words. to do that I used a function maxArray(array, sizeof array) that gives the biggest number in the array in order to count how many times the letter is repeated and store the info in another array in the same position of each letter in the string. But in the two algorithms I have came up with it doesn't work.
PS: I am just a beginner.
Here is the code:
int maxArray(int *tab, int n) {
int i, tmp;
tmp = tab[0];
for (i = 1; i < n; i++) {
if (tmp < tab[i])
tmp = tab[i];
}
return tmp;
}
//first algo(didn't finish it)
char occurencedelettre(char *string) {
int *array;
int i, j, compt, max;
for (i = 0; string[i] !='\0'; i++) {
compt = 0;
for (j = 0; string[j] !='\0'; j++) {
if (string[i] == string[j])
compt++;
}
array[i] = compt;
}
return array;
}
//second one
char occurencedelettre(char *string) {
int count[25] = { 0 };
int x = 0;
char result;
for (int i = 0; string[i] != '\0'; i++) {
count[string[i]]++;
if (x < count[string[i]]) {
x = count[string[i]];
result = string[i];
}
}
return result;
}

Answer 1

The second approach is almost correct except for these problems:
the array should have a length of 26
you must subtract 'A' from the value of the letter to get an index between 0 and 25, assuming the word only contains uppercase letters in ASCII.
you must intialize result to return 0 (or any other specific value) for an empty word.
Here is a modified version:
char occurencedelettre(const char *string) {
size_t count[26] = { 0 };
size_t x = 0;
char result = '\0';
for (size_t i = 0; string[i] != '\0'; i++) {
count[string[i] - 'A']++;
if (x < count[string[i]]) {
x = count[string[i]];
result = string[i];
}
}
return result;
}
The first approach is more cumbersome and slower, but also more generic as it may work for any word contents. Here is a modified version:
char occurencedelettre(const char *string) {
char result = 0;
size_t max_count = 0;
for (size_t i = 0; string[i] != '\0'; i++) {
size_t count = 1;
for (size_t j = i + 1; string[j] != '\0'; j++) {
if (string[i] == string[j])
count++;
}
if (max_count < count) {
max_count = count;
result = string[i];
}
}
return result;
}
Note that you can adapt the first approach for any word contents, assuming 8-bit bytes:
char occurencedelettre(const char *string) {
size_t count[256] = { 0 };
size_t x = 0;
char result = '\0';
for (size_t i = 0; string[i] != '\0'; i++) {
count[(unsigned char)string[i]]++;
if (x < count[(unsigned char)string[i]]) {
x = count[(unsigned char)string[i]];
result = string[i];
}
}
return result;
}