C program to find maximum occurrence of character in a string

In C programming, finding the character with maximum occurrence in a string involves counting the frequency of each character and determining which appears most often. This is useful for text analysis and character statistics.

Syntax

int frequency[ASCII_SIZE];
while(string[i] != '\0') {
    frequency[(int)string[i]]++;
    i++;
}

Algorithm

The algorithm to find maximum occurrence follows these steps −

• Initialize a frequency array to count occurrences of each ASCII character
• Traverse the string and increment frequency count for each character
• Find the character with maximum frequency count

Example: Complete Program

Here is a complete C program to find the character with maximum occurrence in a string −

#include <stdio.h>
#include <string.h>

#define CHARS 256

int main() {
    char string[] = "tutorials point";
    int frequency[CHARS] = {0};
    int i, maximum = 0;
    
    printf("Input string: %s<br>", string);
    
    /* Count frequency of each character */
    for (i = 0; string[i] != '\0'; i++) {
        frequency[(int)string[i]]++;
    }
    
    /* Find character with maximum frequency */
    for (i = 0; i < CHARS; i++) {
        if (frequency[i] > frequency[maximum]) {
            maximum = i;
        }
    }
    
    printf("Maximum occurrence character is '%c' = %d times<br>", 
           maximum, frequency[maximum]);
    
    return 0;
}

Input string: tutorials point
Maximum occurrence character is 't' = 3 times

Example: Interactive Version with User Input

This version allows user to input their own string −

#include <stdio.h>
#include <string.h>

#define SIZE 100
#define CHARS 256

int main() {
    char string[SIZE];
    int frequency[CHARS] = {0};
    int i, maximum = 0;
    
    printf("Enter a string: ");
    fgets(string, SIZE, stdin);
    
    /* Remove newline if present */
    string[strcspn(string, "<br>")] = '\0';
    
    /* Count frequency of each character */
    for (i = 0; string[i] != '\0'; i++) {
        frequency[(int)string[i]]++;
    }
    
    /* Find character with maximum frequency */
    for (i = 0; i < CHARS; i++) {
        if (frequency[i] > frequency[maximum]) {
            maximum = i;
        }
    }
    
    printf("Maximum occurrence character is '%c' = %d times<br>", 
           maximum, frequency[maximum]);
    
    return 0;
}

Key Points

• The frequency array size should be 256 to handle all ASCII characters
• Initialize the frequency array to zero before counting
• Use fgets() instead of gets() for safe input handling
• Time complexity is O(n) where n is the string length
• Space complexity is O(1) as the frequency array size is constant

Conclusion

Finding the maximum occurring character in C requires counting character frequencies and identifying the maximum. This approach efficiently handles all ASCII characters with linear time complexity.