How to get int from char in C

Question

(i'm french, sorry for my bad english)

I don't know how to get an int from a char[], the patern of the char will be the same everytime : "prendre 2", "prendre 44", "prendre 710"...

I want to check if the pattern of the sentence is correct and get the integer.

I have try to do this, but as you see, the problem is i just can check if the integer is between 0-9 because I check only one char.

[...]

else if (est_prendre(commande)){
    /* if  the output is 1*/
    int number = commande[8]- '0'
}

int est_prendre(char *commande){
    int i;
    char temp[9] = "";
    char c = commande[8];
    int num = c - '0';
    for (i=0; i<8; i++){
        temp[i] = commande[i];
    }
    if (strcmp ("prendre ", temp) == 0)
    {
        if ( /*  num IS INTEGER?  */)
        {
            return 1;
        }
        else
        {
            return 0;
        }
    } else {
        return 0;
    }

}

I expect if commande = "prendre 3", output of est_prendre is 1 because the pattern is correct And after than to put the integer into the variable number.

Thank You!

Roberto Caboni · Answer 1 · 2019-04-15T11:48:17.780

2

Assuming that 'commande + 8' is a valid substring, what you need is atoi() function (ASCII to Integer). This function is widely documented, and you can easily find online its usage.

int number = atoi(commande+8);

Just remember that the substring terminates at the first non-digit character:

atoi("23") returns 23
atoi("51hh37") returns 51
atoi("z3456") returns 0

Note: atoi converts input string into integer, and you can use it if you are sure it fits expected input. So, if you expect to have either long integers or float values in your string you can use atol() (ASCII to long) or atof() (ASCII to float).

edited Apr 15 '19 at 11:48

answered Apr 15 '19 at 10:15

Roberto Caboni

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[**Why shouldn't I use atoi()?**](https://stackoverflow.com/questions/17710018/why-shouldnt-i-use-atoi) – Andrew Henle Apr 15 '19 at 10:26
1

`commande[8]` is a `char`, not a string. You probably wan't to use `commande + 8`. – HAL9000 Apr 15 '19 at 11:09
@HAL9000 you're right. I did a mistake in adapting original code to my example. I just corrected. – Roberto Caboni Apr 15 '19 at 11:43
@AndrewHenle I get your point, but I think atoi is still a valid option if you have control on input format and/or you know exactly what to expect. I think that my answer can be improved just adding a note about the correct ato*() function to be used according to the expected input. – Roberto Caboni Apr 15 '19 at 11:43

score 1 · Accepted Answer · answered Apr 15 '19 at 09:47

This is very basic, you should (re)read any reference/tutorial on C that you have used to learn the language.

You should just use the sscanf() standard function:

int value;
if (sscanf(commande, "prendre %d", &value) == 1)
{
  ... it was a match, the variable 'value' will be set to the number from the string
}

you can delete the (strange-looking) code that copies characters from commande to temp, and the temp variable too of course. Just inspect the commande string directly.

How to get int from char in C

2 Answers2