{"id":1170,"date":"2024-11-11T01:44:18","date_gmt":"2024-11-10T20:14:18","guid":{"rendered":"https:\/\/codexplained.in\/?p=1170"},"modified":"2025-11-24T15:27:51","modified_gmt":"2025-11-24T09:57:51","slug":"c-programming-find-first-unique-character-in-a-string","status":"publish","type":"post","link":"https:\/\/codexplained.in\/?p=1170","title":{"rendered":"C Programming: Find First Unique Character in a String"},"content":{"rendered":"\n

Introduction<\/h2>\n\n\n\n

Finding the first non-repeated (unique) character in a string is a simple yet important problem in programming. In this task, you need to find the first character in a string that doesn’t repeat. <\/p>\n\n\n\n

For example,<\/strong> in the string “swiss,” the first unique character is ‘w’. It appears only once, while<\/strong> ‘s’ repeats. In contrast,<\/strong> in the string “hello,” the first unique character is ‘h’. The characters ‘e’ and ‘l’ repeat. Therefore,<\/strong> finding the first unique character helps solve similar problems in programming.<\/p>\n\n\n\n

This problem helps you practice basic C programming skills like working with strings, arrays, loops, and conditionals.<\/p>\n\n\n\n

Code<\/h2>\n\n\n
\n#include <stdio.h>\n#include <string.h>\n\nchar firstUniqueChar(char str[]) {\n    int count[256] = {0};  \/\/ Array to count occurrences of each character\n\n    \/\/ Count the frequency of each character\n    for (int i = 0; str[i] != '\\0'; i++) {\n        count[str[i]]++;  \/\/ Increment the count for each character\n    }\n\n    \/\/ Find the first character that appears only once\n    for (int i = 0; str[i] != '\\0'; i++) {\n        if (count[str[i]] == 1) {\n            return str[i];  \/\/ Return the first unique character\n        }\n    }\n\n    return '\\0';  \/\/ If no unique character is found, return '\\0'\n}\n\nint main() {\n    char str[] = "swiss";  \/\/ Example string\n    char result = firstUniqueChar(str);\n\n    \/\/ Output the result\n    if (result != '\\0') {\n        printf("The first unique character is: %c\\n", result);\n    } else {\n        printf("No unique character found.\\n");\n    }\n\n    return 0;\n}\n\n<\/pre><\/div>\n\n\n
Input<\/h2>\n\n\n\n
The input is a string. For example:<\/strong><\/p>\n\n\n\n
    \n
  • \"swiss\"<\/code><\/li>\n<\/ul>\n\n\n\n
    Output<\/h2>\n\n\n\n
    The program will print the first character that is unique (appears only once).<\/p>\n\n\n\n
    For the input \"swiss\"<\/code>, the output will be:<\/p>\n\n\n\n
    The first unique character is: w<\/strong><\/p>\n\n\n\n
    If there is no unique character (i.e., all characters repeat), the output will be:<\/p>\n\n\n\n
    No unique character found.<\/strong><\/p>\n\n\n\n
    Explanation<\/h2>\n\n\n\n
    Count Array<\/strong>:
    We use an array count[256]<\/code> to count how many times each character appears in the string. Each index of the array corresponds to an ASCII value of a character.<\/p>\n\n\n\n
    Counting Occurrences<\/strong>:
    In the first loop, we go through each character of the string and increment its count in the count<\/code> array.<\/p>\n\n\n\n
    Finding the First Unique Character<\/strong>:
    After counting, we go through the string again and check if a character appears only once (i.e., count[str[i]] == 1<\/code>). The first such character is the result.<\/p>\n\n\n\n
    Edge Case<\/strong>:
    If there are no unique characters (i.e., all characters repeat), the program will print “No unique character found.”<\/p>\n\n\n\n
    Conclusion<\/h2>\n\n\n\n
    This simple problem helps you practice basic C concepts like arrays, loops, and conditionals. The solution uses a counting method, which makes it efficient with a time complexity of O(n)<\/strong>, where n<\/code> is the length of the string.<\/p>\n