finding most common char in a string

This is a discussion on finding most common char in a string within the C++ Programming forums, part of the General Programming Boards category; I need to find the character that occurs the most in a string (not a char array). The user enters ...

  1. #1
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    finding most common char in a string

    I need to find the character that occurs the most in a string (not a char array). The user enters a string, and from there I thought I could use scanf, but I didn't find anything about scanf that says it could return the most used character. (ie. if someone enters "this is my str" then S would be the most used char).

    Is there a function I'm not aware of that can do this, a better way of doing it, or not possible at all?

  2. #2
    C++ Witch laserlight's Avatar
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    You can use a map<char, int> to map chars to their occurrences. Insert the chars into the map and increment the occurrence for that. When you are done with the insertions, look for the element in the map with the highest occurrence.
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  3. #3
    and the hat of wrongness Salem's Avatar
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    Use an array with as many elements as there are characters to count.
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    Alright, i tried Salem's idea, but it always comes out with 'L' as being the most used char even if there isn't an L in the string. I think it might have to do with turning the string to a char array so I can read each char seperately. I switched the L char to a different letter and it displayed that char. I also took the 'L' out, and typed "ttttt" and it said 'a' was the most common. So is it the strcpy() screwing it up?

    Code:
    char ReturnMostUsed(string* ptr){
    
        char common;
        int size = sizeof(ptr), count = 0;
        char line[size+1];
        int a=0,b=0,c=0,d=0,e=0,f=0,g=0,
            h=0,i=0,j=0,k=0,l=0,m=0,n=0,
            o=0,p=0,q=0,r=0,s=0,t=0,u=0,
            v=0,w=0,x=0,y=0,z=0;
    
        strcpy(line,(char*)ptr);
    
        while(count <= size){
    
            if(isalpha(line[count])){
                if(line[count] == 'a')
                    a++;
    // further down the code it goes through all the possible chars
    // then finds which ever count is highest, then displays that char

  5. #5
    C++まいる!Cをこわせ!
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    You didn't understand the idea. Look here:
    Code:
    int chars[255];
    ZeroMemory(chars, 255);
    char* str = "aaabbbcccddd...zz";
    for (int i = 0; i < strlen(str); i++)
    	chars[str[i]]++;
    Work from that.

  6. #6
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    I'm not understanding this part...
    Code:
    chars[str[i]]++;
    What's the purpose of putting the 'char* str' inside the 'int chars' index? More effectively, what does that accomplish by doing that?

  7. #7
    C++まいる!Cをこわせ!
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    Because char is basically an int. str[i] returns an int, an int that represents the number of the character at that location in the string.

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