initial commit

1 files changed, 137 insertions, 0 deletions

diff --git a/main.c b/main.c
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index 0000000..86a0929
--- /dev/null
+++ b/main.c
@@ -0,0 +1,137 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+/*
+Exercise 2·3. Write the function htoi (s ), which converts a string of hexa-
+decimal digits (including an optional 0x or 0X) into its equivalent integer value.
+The allowable digits are 0 through 9, a through f, and A through F.
+*/
+
+//function to calculate square roots
+unsigned long powq(int number, int power)
+{
+unsigned long 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;//Effectively result=number*number*(number is repeated as many times as the "power" int
+	--power;//--power since a power has been calculated
+	}
+return result;
+}
+
+
+//htoi(): converts a string of hex encoded in ASCII to an integer value. (No negative input num handling, no invalid char handling (treats invalid chars like a '0') and ignores overflows)
+unsigned long long htoi(char s[])
+{
+unsigned long long result = 0;//result is by default; 0
+int power = 0;//power is by default; 0
+while(s[power] != '\0'){++power;}//increment power for however many non-null chars in the string.
+--power;//We need 1 less than the number of non-null chars.
+
+int i = 0;//loop variable
+while(s[i] != '\0')//loop until a NULL char
+{
+if (s[i] >= '0' && s[i] <= '9')//if char is a number, add as such
+	{
+	result += ((s[i] - '0') * powq(16,power));//result = result + ([char converted to number] * (16^[e.g. 3...2... etc])
+	goto skip;//no need to check if the chars any other, since we already did so and calculated
+	}
+
+if (s[i] >= 'A' && s[i] <= 'F')//check for digit
+	{
+	result += ((s[i] - 55) * powq(16,power));//result = result + ([char converted to number] * (16^[e.g. 3...2... etc])
+	goto skip;//no need to check if the chars any other, since we already did so and calculated
+	}
+
+if (s[i] >= 'a' && s[i] <= 'f')//check for digit
+	{
+	result += ((s[i] - 87) * powq(16,power));//result = result + ([char converted to number] * (16^[e.g. 3...2... etc])
+	goto skip;//no need to check if the chars any other, since we already did so and calculated
+	}
+
+
+skip: ++i;//increment i to read the next char
+--power;//Deincrement the power. E.g. ([charvalue]*(16^3))+([nextcharvalue]*(16^2)) etc
+}
+
+if (s[0] == '-'){return -result;}//handle negative numbers
+
+return result;//return the converted number
+}
+
+int main(int argc, char *argv[])
+{
+bool negative = false; //handle negative numbers
+if (!argv[1]){goto stdinMode;}
+
+	if (argv[1][1] == '-')
+	{
+	printf("Usage (stdin mode): %s\n", argv[0]);
+	printf("Ctrl+D to exit\n");
+	printf("Usage (cli args mode): %s [hexnum]\n", argv[0]);
+	printf("Licence: AGPLv3\n");
+	return 0;
+	}
+if (argv[1][0] == '-'){negative = true;}//handle negative numbers
+
+//strip out invalid chars from the input string
+int x,y;//counter variables
+for (x=0; argv[1][x] != '\0'; ++x)
+	{
+	if ( ((argv[1][x]>=1)&&(argv[1][x]<='/')) || ((argv[1][x] >=':')&&(argv[1][x]<='@')) || ((argv[1][x]>='G')&&(argv[1][x]<='`')) || ((argv[1][x]>='g')&&(argv[1][x]<=127)) )//if input[i] is an invalid character (dirty but only option)
+		{
+		y=x;//point to overwite equals y
+		while(argv[1][y] != '\0'){argv[1][y++] = argv[1][y+1];}//shift all characters above left, overwriting the character
+		--x;//deincrement x, since the string was just shrunk by one and the one just above could indeed be a matching char
+		}
+	}
+
+
+if (negative){printf("-%llu\n", htoi(argv[1])); return 0;}
+printf("%llu\n", htoi(argv[1]));
+return 0;
+
+stdinMode: ;
+
+int size = 10;
+char *input = malloc(size*sizeof(char));
+if (!input){printf("Malloc failed!\n"); return 1;}
+
+int i;
+nextnum: i=0;
+char c;
+while ((c=getchar())!='\n')
+{
+if (c==EOF){free(input); exit(0);}//exit if EOF
+if (i==size-1){size+=4; input=realloc(input,size*sizeof(char)); if (!input){printf("Realloc failed!\n"); return 1;}}//realloc input array if input is about to overflow it
+input[i]=c;
+++i;
+}
+input[i] = '\0'; //add NULL char for htoi
+
+
+//strip out invalid chars from the input string
+if (input[0] == '-'){negative = true;}//handle negative numbers
+int j;//another counter variable
+for (i=0; input[i] != '\0'; ++i)
+	{
+	if ( ((input[i]>=1)&&(input[i]<='/')) || ((input[i] >=':')&&(input[i]<='@')) || ((input[i]>='G')&&(input[i]<='`')) || ((input[i]>='g')&&(input[i]<=127)) )//if input[i] is an invalid character (dirty but only option)
+		{
+		j=i;//point to overwite equals j
+		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
+		}
+	}
+
+if (negative){printf("Decimal: -%llu\n", htoi(input)); negative = false; goto nextnum;}
+printf("Decimal: %llu\n", htoi(input));
+goto nextnum; //process another number
+
+//never reached, but left in case of the removal of nextnum
+free(input);
+
+return 0;
+}
+