How do I change an array of characters into an array of integers?

Question

More specifically, how do I change'

char tempList[256] = "1 -2 -8 4 5";

into something like this:

int tempListNum[256] = {1, -2, -8, 4, 5};

?

I tried this, but I don't know how to append the array.

for (int j = 0; j < 256; j++)
{
    if(TEMPS[j] == 45 && (TEMPS[j+1] >= 48 && TEMPS[j+2] >= 48))
    {
        numToAppend = ((TEMPS[j+1]-'0')*10 + (TEMPS[j+2]-'0')) * -1;
    }
    if(TEMPS[j] == 45 && TEMPS[j+1] >= 48)
    {
        numToAppend = (TEMPS[j+1]-'0') * -1;
    }
    if(TEMPS[j] >= 48)
    {
        numToAppend = TEMPS[j]-'0';
    }
    if(TEMPS[j] >= 48 && TEMPS[j+1] >= 48)
    {
        numToAppend = TEMPS[j]*10 + TEMPS[j+1];
    }
}

Answer 1

use this: it works on me.

#include <stdio.h>
#include <ctype.h>
#include <math.h>

int main() {
    char tempList[256] = "1 -2 -82 43 5";
    char tempNumber[10];
    int tempNumberCounter = 0;
    int i, j,counter=0, isNegative = 1;
    int numTempList[256] = {0};

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

        if(tempList[i-1] == '-') {
            isNegative = -1;
        }

        if(isdigit(tempList[i])) {
            tempNumber[tempNumberCounter] = tempList[i];
            tempNumberCounter++;
        }

        if(tempList[i] == ' ' || tempList[i+1] == '\0') {
            tempNumber[tempNumberCounter] = '\0';

            for(j=0; j<strlen(tempNumber); j++) {
                numTempList[counter] += (tempNumber[j] - '0') * pow(10, strlen(tempNumber)-j-1);
            }           

            numTempList[counter] *= isNegative;
            counter++;
            tempNumberCounter = 0;
            *tempNumber = 0;
            isNegative = 1;
        }
        
    }

    for(i=0; numTempList[i] != 0; i++) {
        printf("%d ", numTempList[i]);
    }
    return 0;
}

numTempList is the converted array from tempList. this is just a sample implementation of char to int array, you can refactor this into functions so that you can reuse this functionality..

Modified:

Now it can also read multiple digits

Answer 2

You can try this :

char tempList[256] = "1 -2 -8 4 5";
int tempListNum[256]

int i=0,k=0;
while(i<256)
{
  int num=0;
  for(int j=0;tempList[j]!=' ';j++)
  {
    int neg=0,counter=0; //Not worked in C for a long time and I am not sure if it supports Bools
    if(a[j]=='-')
     neg=1;
    else
     num=num*10+int(tempList[j])-int('0');
    counter++;
 }
  if(neg==1)
   num=-num;
  tempListNum[k]=num;
  k++; i+=counter;
}

Answer 3

Consider this short example:

#include <stdio.h> 
#include <stdlib.h>

int main ()
{
  char tempList[256] = "1 -2 -8 4 5";
  int tempListNum[256] = {0};
  int numCnt = 0;
  char * pEnd = tempList;
  int number = 0;
  while( strlen(pEnd) > 0)
  {
    tempListNum[numCnt] = strtol (pEnd,&pEnd,0);
    numCnt++;
  }
  for(number = 0; number < numCnt; number++)
  {
      printf("%d ", tempListNum[number]);
  }
  return 0;
}

Answer 4

For example, with while loop and functions sscanf and strtok from strings.h.

#include <stdio.h>
#include <string.h>
int main (void)
{
    char tempList[256] = "1 -2 -8 4 5";
    int tempListNum[256] = {0};
    int cnt = 0;
    int tmp = 0;
    char * str = strtok (tempList," ");
    while(str != NULL)
    {
        if(sscanf(str, "%d", &tmp))
        {
            tempListNum[cnt] = tmp;
            cnt++;
        }
        // read next number
        str = strtok (NULL," ");
    }
    // test output
    for(tmp = 0; tmp < cnt; tmp++)
    {
        printf("%d ", tempListNum[tmp]);
    }
    return 0;
}

Tested in Visual Studio 2012.

Answer 5

Is this a homework assignment, or maybe a interview question?

I haven't tested this, but you could do something like this:

#define enum _error {
   success = 0,
   parse_error,
   out_of_memory,
   invalid_arg,
   insuficient_buffer
} error;

error parse_int(
   char **pp,
   int *val)
{
   error e = success;
   char neg = 0;

   if (!pp || !*pp || !val) {
      e = invalid_arg;
      goto exit;
   }

   *val = 0;

   while (**pp) {
      if (**pp == '-') {
         if (val) {
            e = parse_error;
            goto exit;
         }

         neg = 1;
      }
      else if (**pp >= '0' **pp <= '9') {
          *val *= 10;
          *val += **pp - '0';
      }
      else {
         break;
      }

      ++*pp; 
   }

   if (neg) {
      *val *= -1;
   }

exit:

   return e;
}

error parse_array_of_ints(
   char *p,
   unsigned int parsed_ints_size,
   int **parsed_ints)
{
   error e = success;
   unsigned int cur = 0;

   if (!p || !parsed_ints) {
      e = invalid_arg;
      goto exit;
   }

   for (;;) {
      while (*p && *p != '-' && *p < '0' && *p > '9') {
         p++;
      }

      if (!*p) {
         break;
      }

      if (cur = parsed_ints_size) {
         e = insuficient_buffer;
         goto exit;
      }

      e = parse_int(&p, parsed_ints+cur);

      if (e != success) {
         goto exit;
      }

      cur++;
   }

exit:

   return e;
}

Answer 6

This isn't terribly difficult. I'd recommend a custom strtoi function instead of atoi since atoi allows for little error handling. For example, atoi("1.3") would return 1 with no other way to get other information like the fact that ".3" makes it not an integer. Moreover, the value 1 is obviously within the range of the int type, so even errno may not be of help.

That is why I write and use strtoi below, which uses the C library's strtol function and has the same behaviors. If you need help understanding what strtoi does, look up documentation for strtol since they're pretty much the same except for the range of valid values (between INT_MIN and INT_MAX, both inclusive, instead of between LONG_MIN and LONG_MAX, both inclusive).

#include <stdio.h>
#include <stdlib.h> //strtol
#include <string.h> //strtok
#include <limits.h> //INT_MIN, INT_MAX
#include <errno.h> //errno, ERANGE

int
strtoi (const char *s, char **rem, int base)
{
  long n;
  int esave = errno;

  errno = 0;
  n = strtol (s, rem, base);
  if (n < INT_MIN || n > INT_MAX)
    errno = ERANGE;

  if (errno)
    {
      if (n == LONG_MAX)
        return INT_MAX;
      return INT_MIN;
    }

  errno = esave;
  return (int) n;
}

int
main (void)
{
  char tempList[256] = "1 -2 -8 4 5";
  int tempListNum[128] = {0};
  int i, n;
  char *listPtr;
  char *listPtr2;

  listPtr = strtok (tempList, " ");
  for (i = 0;
       listPtr != NULL && (size_t) i < sizeof tempListNum / sizeof tempListNum[0];
       ++i)
    {
      errno = 0;
      n = strtoi (listPtr, &listPtr2, 10);

      if (*listPtr2)
        {
          fprintf (stderr, "error: value `%s' is not an integer ... ignoring value\n", listPtr);
          --i;
        }

      // value out of range or some other implementation-defined error
      else if (errno)
        {
          perror (listPtr);
        }

      listPtr = strtok (NULL, " ");
    }

  // n is now the number of items in the array
  n = i;

  for (i = 0; i < n; ++i)
    printf ("%d\n", tempListNum[i]);
}

You could obviously avoid strtok and just use strtoi by itself. That might actually be a cleaner solution!

Answer 7

you can use strtok with space as separator and then use atoi standard library function

Answer 8

You can try this

unsigned char index1 = 0,index2 =0;
int PrevValue = 0;
for(;index1 <= 255;index1 ++)
{
      if(tempList[index1] != ' ') //space
      {
         tempListNum[index2] = PrevValue*10 + (tempList[index1]-0x30);
         PrevValue = tempListNum[index2] ;

      }
      else
      {  
           PrevValue  = 0;
           index2++;
      }

}

You can add further optimizations and other validations.

Answer 9

Write a function that goes through tempList char by char:

• While it encounters only numbers, it should turn them into an int. If there are more than 1 digit, it should multiply the first digit with 10 and add then add it to the int, etc.

• When it encounters a space, it should add the newly created int to tempListNum and skip the space.

• When it encounters a minus sign, it should multiply the currently created int with -1.

• Repeat these steps until end of list.