Count the how many 7 are there between 1 to 100

Write a Program to Count How many times a digit is there in a range

There is a generic formula for this also n(10^(n-1)) where range is 0 to 10ⁿ

/*one generic function to find char count in an string*/
unsigned int count_char_in_str(char ch, const char *str){
        unsigned int count=0;
        while((str=strchr(str, ch))!=NULL){
                count++;
                str+=1;
        }
        return count;
}
/*find single digit count in a series of numbers*/
unsigned int count_digit_in_range(unsigned int digit, unsigned int min , unsigned int max){
        char str_number[1024]={0x00};
        unsigned int count = 0;
        for(int i=min; i < max; i++){
                sprintf(str_number, "%02d", i);
                count += count_char_in_str(digit+0x30, str_number);
                memset(str_number, 0x00, sizeof(str_number));
        }
        return count;
}

Complete Code

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

unsigned int count_char_in_str(char ch, const char *str){
        unsigned int count=0;
        while((str=strchr(str, ch))!=NULL){
                count++;
                str+=1;
        }
        return count;
}
unsigned int count_digit_in_range(unsigned int digit, unsigned int min , unsigned int max){
        char str_number[1024]={0x00};
        unsigned int count = 0;
        for(int i=min; i <= max; i++){
                sprintf(str_number, "%d", i);
                count += count_char_in_str(digit+0x30, str_number);
                memset(str_number, 0x00, sizeof(str_number));
        }
        return count;
}

int main(int argc, char *argv[]){
        int number=7;
        int range_min = 1;
        int range_max = 100;
        printf("%d Times Number %d Coming between %d to %d\n", count_digit_in_range( number, range_min, range_max), number, range_min, range_max);
        return 0;
}

compile and output

rajesh@ideapad:~/Rajesh/Blog/string$ gcc cout_total_number_of_7_coming_serise.c
rajesh@ideapad:~/Rajesh/Blog/string$ ./a.out 
20 Times Number 7 Coming between 1 to 100