What is a string of hexadecimal digits?

Now that the question is answered, I will post my solution using the help that I got from everyone here (THANKS!) The main thing I don't like is assuming every input ends in '\n' just because my linux terminal does! Also there has to be a more elegant way to convert A-F/a-f to decimal, maybe using a helper function that I write myself (don't have access to any functions yet besides pow and printf)! I am doing K&R The C Programming Language, Exercise 2.3: "Write a function, htoi(s), which converts a string of hexadecimal 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." ``` #include <stdio.h> #include <math.h> #define MAXLEN 1000 /* maximum accepted user input is 999 digits */ int htoi( char s[], int maxPower ) ; /* maxPower will be two less than string length (len - 2) because the exponentiation is 0-indexed * remove the length values which represent '\n' and '\0' in user input * if the string begins with "0x" or "0X", we remove two more from the power variable inside the htoi() body. */ int main( void ) { int c, i ; int len ; /* tracks length of hexString, used to determine exponent value */ char hexString[ MAXLEN ] ; len = 0 ; for ( i = 0 ; i < MAXLEN - 1 && ( c = getchar() ) != EOF ; ++i ) { hexString[i] = c ; ++len ; } hexString[len] = '\0' ; /* value of len is one more than termination value of i in above loop */ printf( "Hex String: %s\nInt: %d\n", hexString, htoi( hexString, len - 2 ) ) ; return 0 ; } int htoi( char s[], int power ) { int j, i, n, decimal ; n = 0 ; if ( s[0] == '0' && ( s[1] == 'x' || s[1] == 'X' ) ) { /* cutting off first two array values if string begins with 0x or 0X */ j = 0 ; while ( ( s[j] = s[j + 2] ) != '\0' ) { ++j ; } power = power - 2 ; /* maximum exponent value now represents the usable data */ } for ( i = 0 ; s[i] != '\n' && s[i] != '\0' ; ++i ) { if ( s[i] >= '0' && s[i] <= '9' ) { decimal = s[i] - '0' ; n = ( decimal * pow( 16, power ) ) + n ; --power ; } else if ( s[i] == 'A' || s[i] == 'a' ) { decimal = 10 ; n = ( decimal * pow( 16, power ) ) + n ; --power ; } else if ( s[i] == 'B' || s[i] == 'b' ) { decimal = 11 ; n = ( decimal * pow( 16, power ) ) + n ; --power ; } else if ( s[i] == 'C' || s[i] == 'c' ) { decimal = 12 ; n = ( decimal * pow( 16, power ) ) + n ; --power ; } else if ( s[i] == 'D' || s[i] == 'd' ) { decimal = 13 ; n = ( decimal * pow( 16, power ) ) + n ; --power ; } else if ( s[i] == 'E' || s[i] == 'e' ) { decimal = 14 ; n = ( decimal * pow( 16, power ) ) + n ; --power ; } else if ( s[i] == 'F' || s[i] == 'f' ) { decimal = 15 ; n = ( decimal * pow( 16, power ) ) + n ; --power ; } else { printf( "ERROR 69:\nInput string was not hexidecimal (0-9, A-F, a-f)\nResult is 0!\n" ) ; n = 0; return n; } } return n ; } ```