How to separate character and number from string in c program - c

Question

For example, I want to separate the string "0013subdivision" into 0013 (as an integer that can do addition, subtraction, etc. not char) and subdivision (as a char itself) in the given string.
This is my code so far:
#include <stdio.h>
#include <stdlib.h>
char location[10]; /* for the input with number and letter */
char x;
int house[10]; /* for the integer that will be separated from the string */
int main()
{
printf("Input: ");
scanf ("%s", &location[x]);
x=0
for (x=0; location[x]!='\0'; x++ );
return 0;
}
Based on my research, the code atoi is used to convert the converted value back to int (if I'm not mistaken) but I don't know when to place the function.

Answer 1

location is char array, if you are reading as string use only %s with string name only, index not required.
scanf ("%s", &location[x]); --> scanf ("%s", location);
After separating only int from char array you need to store one int value into house.
int house[10] --> int house.
Here is the code for extracting only int from string :
char location[10]; /* for the input with number and letter */
int x;
int house = 0 ; /* for the integer that will be separated from the string */
int main()
{
printf("Input: ");
//scanf ("%s", &location[x]);
scanf ("%s", location);
for (x=0; location[x]!='\0'; x++ ) {
if(location[x]>='0' && location[x]<='9') {
house =(house * 10) + (location[x]-48);
}
}
printf("int part = %d \n",house);
return 0;
}

Answer 2

The main problem in the code is
scanf ("%s", &location[x]);
Where you did not impose any limit on the scanning. An input like 0013subdivision will cause out of bound memory access leading to undefined behavior.
Always limit the input size with the length modifier, like, for an array defined as
char location[10]
use the conversion specification like
scanf ("%9s", location); // (i) one element saved for terminating null
// (ii) the array name decays to the pointer to 1st element
//in case of an argument to a function call.
Then, you don't need an integer array to store the extracted integer. A singular variable would suffice.
However, i'd like to suggest a much robust way:
read the user input using fgets()
then, scan the input using sscanf() and appropriate conversion specifier, like %4d%9s or alike.

Answer 3

The most correct way to do this is to use the strto... family of functions from stdlib.h. For example:
printf("%ld\n", strtol(str, NULL, 10));
The atoi family of functions should never be used for any purpose, since they have broken error handling and can be 100% replaced by the strto... functions.
You could use the scanf family of functions but they are needlessly slow and notoriously dangerous, so I don't really see the point of using them here.
If you are interested in implementing the actual copying manually, for learning purposes, it is fairly trivial:
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
int main (void)
{
const char str[] = "0013subdivision";
char number_part [sizeof(str)];
char letter_part [sizeof(str)];
size_t i;
for(i=0; str[i]!='\0' && isdigit(str[i]); i++) // find where the letters start
{}
memcpy(number_part, &str[0], i); // copy digit part
number_part[i] = '\0'; // append null terminator
memcpy(letter_part, &str[i], sizeof(str)-i); // copy letter part + null term
puts(number_part);
puts(letter_part);
printf("%ld\n", strtol(str, NULL, 10));
}
If the string is a run-time variable, you have to use strlen(str)+1 instead of sizeof().

Answer 4

strtol converts string to number and also gives you back the character it stopped on, i.e. first character after number.
#include <stdio.h>
#include <stdlib.h>
int main(void) {
const char* const input = "0013subdivision";
const char* string;
const long number = strtol(input, &string, 10);
printf("Number: %ld String: '%s'\n", number, string);
// Number: 13 String: 'subdivision'
return 0;
}
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