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C program to find repeated characters in a string

c program to find repeated characters in a string.

#include<stdio.h>
 
int main(){
    char str[40];
    int i, j = 0;
    scanf("%s", str);
    for(i = 1; str[i] != '\0';i++){
        if(str[i-1] == str[i]){//For consecutive repeated characters
            j = i-1;        //If found, we place an index j there
            j++;
            while(1){           //This loops checks for mutiple
                if(str[j] == str[j+1])  //occurrences of a character
                    j++;
                else
                    break;
            }
            printf("Character %c is repeated %d times\n", str[i], j - (i-1)+1);
            i = j;
        }
    }
    if(j == 0){
        printf("No repeated character");
    }
    return 0;
}

If you wanna find out all the repeated characters, first sort the string lexicographically.
Then use the logic used in the above program to find repeated characters and their number of occurrences

How can we do that with a two dimensional array [12][40]?