How to convert from ASCII to INT

Question

I have a string "a" with numbers on it (e.g "I have 4 apples") and I'm trying to get the number "4" into an int variable without it giving me the ASCII code, in this case "52"(ASCII 4 is 52).

I have tried int y = (int)a[8] but it doesn't work.

try `atoi` https://www.cplusplus.com/reference/cstdlib/atoi/ — Raildex, Feb 08 '21 at 14:09
Another question like this: https://stackoverflow.com/questions/439573/how-to-convert-a-single-char-into-an-int — Yksisarvinen, Feb 08 '21 at 14:12
**You need first to specify** (on paper, using [EBNF notation](https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form)...) **the acceptable inputs**. In your case, is *"j'ai 4 pommes"* (the same phrase in French) an acceptable input? Once you can specify the valid input, you can start to write C++ code. You may want to read the [*Dragon book*](https://en.wikipedia.org/wiki/Compilers:_Principles,_Techniques,_and_Tools) — Basile Starynkevitch, Feb 08 '21 at 14:15
You could also start a PhD in [Natural Language Processing](https://en.wikipedia.org/wiki/Natural_language_processing). For that, find a good enough PhD advisor — Basile Starynkevitch, Feb 08 '21 at 14:19
Any kind of additional information (as requested in comments) is best [edit]ed into the question, instead of hidden down here in the comments. — Yunnosch, Feb 08 '21 at 14:28

prog-fh · Answer 1 · 2021-02-08T14:28:08.417

If the message is supposed to have the exact shape you gave as an example, then you can try the first part of the code below.

The sscanf() function analyses a string and can match literals as well as values you extract in variables.

edit
A more flexible version is provided too, in order to detect an integer anywhere in the string. The idea is to extract the words one by one with %s and skip them thanks to the end position known with %n, until such a word is considered as an integer.

/**
  gcc -std=c99 -o prog_c prog_c.c \
      -pedantic -Wall -Wextra -Wconversion \
      -Wc++-compat -Wwrite-strings -Wold-style-definition -Wvla \
      -g -O0 -UNDEBUG -fsanitize=address,undefined
**/

#include <stdio.h>

int
main(void)
{
  // fixed shape for the message
  const char *msg="I have 4 apples";
  int number=-1;
  if(sscanf(msg, "I have %d apples", &number)==1)
  {
    printf("number=%d\n", number);
  }
  // more flexible version
  const char *msg2="Number 5 appears here";
  while(*msg2!='\0')
  {
    char word[20]="";
    int pos=-1;
    sscanf(msg2, "%s%n", word, &pos);
    int number=-1;
    if(sscanf(word, "%d", &number)==1)
    {
      printf("number=%d\n", number);
      break;
    }
    msg2+=pos; // skip this word
  }
  return 0;
}

Yes, this code works for what I asked, thanks! – Just Dragos Feb 08 '21 at 14:16 — Just Dragos, Feb 08 '21 at 14:16

score 1 · Answer 2 · answered Feb 08 '21 at 14:12

1

The way that I tend to do this is to subtract '0' from it.

e.g.

char x = '8';
int y = x - '0';

A char is normally just an int and ASCII for digits is consecutive, so if you can get the offset from '0' to your digit, you get the value of the digit.

answered Feb 08 '21 at 14:12

Hive7

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How to convert from ASCII to INT

2 Answers2