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/* Copyright (C) 2020 Gentoo-libre Install
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define DEFAULT_SIZE 40 //default size, not too big, not too small
bool negative = false;
//modulo() modulo to return remainder instead of remainder, may not work if N is negative
long long modulo(long long x,long long N)
{
return (x % N + N) % N;
}
//powq(): square roots
long long powq(long long number, long long power)
{
int result = 1;//result int, 1 by default
if (!power){return 1;}//if to the power of 0, return 1
while(power)//loop until all powers have been calculated
{
result *= number;//in the end result=number*number*number*etc until power is reached
--power;//--power since a power has been calculated
}
return result;
}
//mod(): Converts ASCII string to int and calculates modulus while showing working.
void mod(char s[], char *result, int length)
{
if (s[0] == '\0'){printf("Error\n"); return;}//catch case of blank input
char *modChar = strstr(s, "m");//find place of 'm' in string (marker for mod)
if (!modChar){printf("Error\n"); return;}//if m not found, return blank string
++modChar;//point to the character above 'm'
int power = 0; //int to store the power.
while(s[power] != 'm'){++power;}//increment power for however many non-null chars in the string.
--power;//The correct power is actually one less than above returns
int i = 0;//counter int
long long integer = 0;//where the converted int is stored
while (s[i] != 'm')//convert the string of decimal numbers into a int
{
if (s[i] >= '0' && s[i] <= '9'){integer += ((s[i] - '0') * powq(10,power));}//integer = integer + ([char converted to number] * (10^[position of number in string]))
++i;
--power;//Deincrement the power. E.g. ([charvalue]*(10^3))+([nextcharvalue]*(10^2)) etc
}
if (negative){integer = -integer;}
int modPower = 0; //int to store the mod power.
while(modChar[modPower] != '\0'){++modPower;}//increment power for however many non-null chars in the string.
--modPower;//The correct power is seems to be 2 less than above returns (???)
i = 0;
long long modulus = 0;//where the converted modulus is stored
while (modChar[i] != '\0')//convert the string of decimal numbers into a int
{
if (modChar[i] >= '0' && modChar[i] <= '9'){modulus += ((modChar[i] - '0') * powq(10,modPower));}//modulus = modulus + ([char converted to number] * (10^[position of number in string]))
++i;
--modPower;//Deincrement the power. E.g. ([charvalue]*(10^3))+([nextcharvalue]*(10^2)) etc
}
//printf("Number: %lld\n", integer);
//printf("Modulus: %lld\n", modulus);
double fraction = (double)integer;//the modulus working steps are done on fraction since they require decimal points
if (!modulus){printf("Modulus 0 is undefined\n"); return;}
i = 0;
if (!negative)
{
//should be pretty self explainatory
fraction /=modulus;
printf("0. %lld / %lld = %lf\n", integer, modulus, fraction);
printf("1. %lf - %lld = %lf\n", fraction, integer/modulus, fraction - (integer/modulus));
fraction -= (integer/modulus);
printf("2. %lf * %lld = %lf\n", fraction, modulus, fraction*modulus);
}
else
{
printf("int r = integer%%modulus;\nreturn r<0 ? r+m : r;\n"); negative = false;
}
//just solve it directly
//printf("Answer: %u\n", integer % modulus);
printf("Answer: %lld\n", modulo(integer,modulus));
}
int main(int argc, char *argv[])
{
if ((argv[1]) && (argv[1][0] == '-'))
{
printf("Usage: [firstnum] mod [secondnum]\n");
printf("Or: [firstnum]m[secondnum]\n");
printf("This program solves modulus with working.\n");
printf("Ctrl+D to exit\n");
printf("Licence: AGPLv3\n");
return 0;
}
char input[DEFAULT_SIZE];//input string is DEFAULT_SIZE in length
//result string
char *result = malloc(DEFAULT_SIZE*sizeof(char));
if (!result){printf("Malloc failed!\n"); return 1;}
result[DEFAULT_SIZE-1]='\0';//add null terminating char
int i;
nextnum: i=0;
char *character = fgets(input, DEFAULT_SIZE, stdin);
if (!character){free(result); exit(0);}//exit if EOF (fgets() returns -1 on EOF or error)
character = strstr(input,"\n");//try to find the newline in the input so it can be overwritten
if (!character){printf("Input too long\n"); while(getchar() != '\n'); goto nextnum;}//if more than 40 chars were read, input was too long
character = '\0'; //overwrite newline with null char
//strip out invalid chars from the input string
if (input[0] == '-'){negative = true;}
int j;//another counter variable
for (i=0; input[i] != '\0'; ++i)
{
if ((input[i] < '0')||(input[i] > '9') && (input[i] != 'm') )//if input[i] is an invalid character
{
j=i;
while(input[j] != '\0'){input[j++] = input[j+1];}//shift all characters above left, overwriting the character
--i;//deincrement i, since the string was just shrunk by one and the one just above could indeed be a matching char
}
}
//printf("Input: %s\n", input);
mod(input, result, DEFAULT_SIZE-1);
//printf("Result: %s\n", result);
goto nextnum;
//this wont be reached, but included anyway in case the above goto is removed
free(result);
return 0;
}
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