Question

C program help

4. Write a function called scan_hex. Here is its prototype:

void scan_hex(int *xptr);

Here is an example of its use, in conjunction with print_decimal. Assume that the user will type a non-negative hex number as input. Also, assume that the “digits” a-f are in lower case. Let’s say the user types 1b

int x;

scan_hex(&x);

print_decimal(x);

MODIFY THIS CODE

// function inputs a non-negative integer and stores it into *xptr.

// The format of the input is a base 16.

void scan_hex(int *xptr) {

     char buffer[256];

     char newline;

     *xptr = 0;

     scanf("%s%c", buffer, &newline); // get rid of the \n after the input

   

     // you do the rest

}   

The above code should print 27

Answer 1

#include <stdio.h>

void scan_hex(int *xptr)

{

char buffer[256];

char newline;

int i,j,k,sixteen=1;

*xptr = 0;

scanf("%s%c", buffer, &newline);

for(i=0;buffer[i]!='\0';i++);

for(j=i-1;j>=0;j--)

{

if(buffer[j]>='a' && buffer[j]<='f')

{

k = buffer[j] - 87;

// to covert a=10,b=11,c=12,d=13,e=15,f=15

// printf("%d\n",buffer[j]-87);

}

else

{

k = buffer[j] - 48;

//to covert char (1-9) to int(1-9)

// printf("%d\n",buffer[j]-48);

}

//this is to convert in base 16

//if a number is of the form a4,a3,a2,a1 then *xptr = a1*(16)^0 + a2*(16)^1 + a3*(16)^2 + a4*(16)^3

*xptr = *xptr + k * sixteen;

sixteen*=16;

}

}

void print_decimal(int x)

{

printf("%d\n",x);

}

int main()

{

int x;

scan_hex(&x);

print_decimal(x);

}