cs240/labs/lab3/task2/convert.c

/*
 * This is a convert program that takes a base and a POSITIVE number in that base
 * as arguments. It converts the number to decimal and also converts the resulted 
 * decimal back to the original base number.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "convert.h"

char baseChars[25];

int main(int argc, char** argv){
    int base, decimal_num;
    if (argc < 3) {
        printf("Usage: convert <base> <number-to-convert>\n");
        exit(1);
    }
    
    base = atoi(argv[1]);
    
    /*
     * First we need to check whether the input number is valid
     * Say if base is 2 and input number is 35, which is not a binary
     */ 
    validateInput(base, argv[2]);
    
    // Convert the base number to decimal
    decimal_num = convertToDecimal(base, argv[2]);
    printf("Converted to decimal: %d\n", decimal_num); 
    
    // Convert the decimal number back to the base number
    convertToBase(decimal_num, base);
	
    return 0;
}

/*
 * Check if the user inputs are valid
 */
void validateInput(int base, char num[]){
    printf("Number read in base %d: %s\n", base, num);

    // First check whether base is valid
    if (base < 2 || base > 25){
        printf("Invalid base!!\n");
        exit(1);
    }

    // Check if number is positive and if it has valid length
    if (strlen(num) > 32 || num[0] == '-'){
        printf("Invalid input number!!\n");
        exit(1);
    }
    
    // Initialize our base char array for later use
    setBaseChars();

    // Check if the input number matches the base
    int i = 0, j = 0;
    int isValid = 0;
    while (j < strlen(num)) {
        for (i = 0; i < base; i++){
          if  (toupper(num[j]) == baseChars[i]){
            isValid = 1;
          }
        }
        if (!isValid){
            printf("Wrong digit in number!!\n");
            exit(1);
        }
        isValid = 0;
        j++;
    }
    
}

/*
 *  Make baseChars filled with all the chars used in different bases
 */
void setBaseChars() {
    char m = '0';
    int i = 0;
    for (i = 0; i < 10; i++){
        baseChars[i] = m;
        m++;
    }
    
    m = 'A';
    for (i = 10; i < 25; i++){
        baseChars[i] = m;
        m++;
    }
}

/*
 * Convert number in given base to decimal
 */
int convertToDecimal(int base, char num[]){
    /*
	 *	TODO: Write the code to convert input number to decimal(Hint: use given
	 *	function my_pow)
	 */

	int pos = 0;
	int result = 0;
	int len = strlen(num);

	int i = len - 1;
	while (i >= 0) {
		char c = num[i];
		
		int value;
		
		if (c >= 'A' && c <= 'Z') {
			value = c - 'A' + 10;
		} else if (c >= 'a') {
			value = c - 'a' + 10;
		} else {
			value = c - '0';
		}

		//printf("%d += %d^%d * %d = %d\n", result, base, pos, value, my_pow(base, pos) * value);

		result += my_pow(base, pos) * value;

		pos++;
		i--;
	}

	return result;
}

/*
 * Convert decimal back to the given base number
 */
void convertToBase(int num, int base){
	/*
	 *	TODO: Write the code to convert decimal back to the input number
	 *
	 */
	
	/*int length = 0;
	int remaining = num;
	do {
		length++;
		remaining /= 10;
	} while (remaining > 0);*/
	
	char result[32];
	//result[31] = '\0';

	int index = 0;
	int remaining = num;
	do {
		int digit = remaining % base;
		
		if (base >= 16 && digit >= 10) {
			result[index] = (char) ((digit - 10) + 'A');
		} else {
			result[index] = (char) (digit + '0');
		}

		remaining /= base;
		index++;
	} while(remaining > 0);
	
	result[index] = '\0'; // Cut off the rest with null char.
	
	int length = index;
	char newResult[length + 1];
	int i = length;
	int j = 0;
	while (i > 0) {
		newResult[j] = result[length - (j+1)]; 
		//char temp = result[i];
		//result[i] = result[length - i];
		//result[length - i] = temp;
		j++;
		i--;
	}

	newResult[length] = '\0';

	printf("Converted back to base %d: %s\n", base, newResult);

}

/*
 * Return result of power calculation in math
 */
int my_pow(int base, int n){
    int s = 1;
    int i;
    for (i = 0; i < n; i++){
        s *= base;
    }
    return s;
}