Thread: Count number of occurrences of each character in input

  1. #1
    Registered User
    Join Date
    Oct 2020
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    69

    Count number of occurrences of each character in input

    I want to count the number of occurrences of each character found in the input and print it to the output.
    Code:
    #include <stdio.h>
    #include <string.h>
    int main(int argc, char **argv)
    {
        unsigned int countChars = 0, i = 0, k = 0;
        char c, s[100], str[100];
        str[k] = '\0';
        while((c = fgetc(stdin)) != EOF)
        {
            s[i++] = c;
            countChars++;
        }
    //    printf("%s\n", s);
        for(int i = 0; i < strlen(s); i++)
        {
            unsigned int countOccurrences = 1;
            for(int j = i+1; j <= strlen(s); j++)
            {
                if(s[i]==s[j])
                {
                    countOccurrences++;
                }
                    /*if(strchr(str, s[i]) == NULL)
                    {
                        str[k] = s[i];
                        k++;
                    }
                }
                for(k = 0; k < strlen(str); k++)
                {
                    fprintf(stdout, "The character %c has %u occurrences.\n", str[k], countOccurrences);
                }*/
            }
            fprintf(stdout, "The character %c has %u occurrences.\n", s[i], countOccurrences);
        }
    
    
        return 0;
    }
    So far for the input:
    john eats apples
    Output
    The character j has 1 occurrences.
    The character o has 1 occurrences.
    The character h has 1 occurrences.
    The character n has 1 occurrences.
    The character has 2 occurrences.
    The character e has 2 occurrences.
    The character a has 2 occurrences.
    The character t has 1 occurrences.
    The character s has 2 occurrences.
    The character has 1 occurrences.
    The character a has 1 occurrences.
    The character p has 2 occurrences.
    The character p has 1 occurrences.
    The character l has 1 occurrences.
    The character e has 1 occurrences.
    The character s has 1 occurrences.
    The character
    has 1 occurrences.
    The character  has 1 occurrences.

    So I need to add the characters in an array an check that each character appears only once in the array. I tried doing that with strchr and but only garbage was printed. Any ideas?

  2. #2
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    May 2012
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    This isn't the only problem, but fgetc() returns int (not char), so c also needs to be declared as int.

  3. #3
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    Oct 2020
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    69
    Okay, so if I declare c as an int could implement the same logic and just typecast c to char?

  4. #4
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    Sep 2020
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    I think you need to learn how to enable warnings in your code flags. Your code has quite a few errors.

    clang -Wall -Wextra -Wshadow -Wpedantic -Werror -std=c99 -fsanitize=address,undefined -c main.c
    main.c:15:13: error: declaration shadows a local variable [-Werror,-Wshadow]
    for(int i = 0; i < strlen(s); i++)
    ^
    main.c:6:34: note: previous declaration is here
    unsigned int countChars = 0, i = 0, k = 0;
    ^
    main.c:15:22: error: comparison of integers of different signs: 'int' and 'unsigned long long' [-Werror,-Wsign-compare]
    for(int i = 0; i < strlen(s); i++)
    ~ ^ ~~~~~~~~~
    main.c:18:28: error: comparison of integers of different signs: 'int' and 'unsigned long long' [-Werror,-Wsign-compare]
    for(int j = i+1; j <= strlen(s); j++)
    ~ ^ ~~~~~~~~~
    3 errors generated.

  5. #5
    Registered User
    Join Date
    Feb 2021
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    6
    Code:
    #include <string.h>
    #include <stdlib.h>
    #include <stdio.h>
    
    void countOccurrences(char* str)
    {
        // 1) Count occurrences.
        int occurrences[256] = {0};
        for(; *str; str++)
            occurrences[(unsigned char) *str]++;
    
    
        // 2) Print occurences.
        for(size_t i = 0; i < 256; i++)
            if(occurrences[i])
                printf("'%c' occurs %d times\n", (char) i, occurrences[i]);
    }
    
    int main()
    {
        countOccurrences("Hello World");
        return 0;
    }
    Code:
    ' ' occurs 1 times
    'H' occurs 1 times
    'W' occurs 1 times
    'd' occurs 1 times
    'e' occurs 1 times
    'l' occurs 3 times
    'o' occurs 2 times
    'r' occurs 1 times
    This counts and prints the unique occurrences of each char in str, which is probably what you wanted? Notice that the entire string needs to be in memory for this to work, which is more than is strictly necessary for your situation. Another implementation would be:

    Code:
    int main()
    {
        // 1) Count occurrences.
        int c, occurrences[256] = {0};
        while((c = fgetc(stdin)) != EOF)
            occurrences[(unsigned char) c]++;
        
        // 2) Print occurrences.
        for(size_t i = 0; i < 256; i++)
            if(occurrences[i])
                printf("'%c' occurs %d times\n", (char) i, occurrences[i]);
    
        return 0;
    }

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