Number converter

main.c

/*
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 */

/* 
 * File:   main.c
 * Author: Сергій Шнуренко
 *
 * Created on 9 березня 2016, 22:31
 */

#include <stdio.h>
#include <math.h>

char* convert(char* arg,int base_from, int base_to);
char check(char * input, int base_from);

char* symb_array = "0123456789ABCDEF";

int main(int argc, char** argv) {
    //analyzing arguments
    
    char* input = argv[3];
    int b_f = atoi(argv[1]);
    int b_t = atoi(argv[2]);
    
    //int b_f = 10;
    //int b_t = 10;
    //char* input = "11111111";
    
    if(b_f<2 || b_f>16||b_t<2 || b_t>16){
        printf("Base of system must be in range of 2-16");
        return 1;
    }
    //checking if number we want translate is corresponds
    if(!check(input,b_f)){
        printf("%s is not correct format for the %d system",input,b_f);
        return 1;
    }
    
    char* output_string = convert(input,b_f,b_t);
    printf(output_string);
    return (0);
}
/*
 *returns true, if input is correspond to base
 */
char check(char * input, int base_from){
    int i;
    //going throught the input array
    for(i=0; i<strlen(input); i++){
        //input is not allowing to have :;<=>?@ symbols
        if(input[i]>'9' && input[i]<'A')
            return 0;
            
        //checks if element is in the correct range according to base_from
        if(input[i]<'0' || input[i]>symb_array[base_from-1])
            //value of input is not in correct range
            return 0;
    }
    //all right check is done
    return 1;
}

/*
 *Converts bas_from format to base_to format 
 */
char* convert(char* arg,int base_from,int base_to) {
    int i;
    long number = 0;
    //converting number from char sequence to long
    for(i = 0; i < strlen(arg); i++){
        //in case of digit lying in range 0..9
        if(arg[i]>='0' && arg[i]<='9')
            number = number * base_from + arg[i] - '0';
        else if(arg[i]>='A' && arg[i]<='F')
            number = number * base_from + arg[i] - 'A' + 10;
    }
    
    //calculating the size of the string(also index of lower digits)
    //formula equals to lOG_base_to of number + 1(value itself)
    //+1 null string terminator
    int current_index = (int) (log(number)/log(base_to)) + 2;
    
    char* output_string = (char*)malloc(current_index*sizeof(char));
    output_string[--current_index] = '\0';
    //converting from int to output format
    while(number>0){    
        int digit = number % base_to;
        output_string[--current_index] = symb_array[digit];
        number =number /base_to;
    } 
    return output_string;
}