How do we cast an argv[]

[Abdi]

Hi everyone,

I would like to know how do we cast an argv[] if I want to check
whether it is equal to some integer number or decimal in C ?

another question what is the difference between unsigned char and char ?

[sean345]

To turn a string like argv[0] or argv[x] into a integer you can use atoi(String). Use atof if you want to convert a string to a float.

- Sean

[shaik786]

A variable declared as char is capable of storing any integer between the values: -128 to +127
While, a variable declared as unsigned char is capable of storing any integer between the values: 0 to 255
This kind of working is due to the fact that a 'char' consists of 8 BITS (1 BYTE), the Most Significant Bit (MSB) of which is used to represent it's sign (+ or -).
In the case of a 'char', when this bit is set to '1', the number is assumed to be a negative number, and when '0', is assumed to be a positive number.
But in the case of 'unsigned char', the MSB is not used for terming the number a -ve or a +ve, instead, the number is presumed always to be a +ve integer.

[Hammer]

Originally posted by sean345
To turn a string like argv[0] or argv[x] into a integer you can use atoi(String). Use atof if you want to convert a string to a float.

Just to be pedantic , it's pretty unlikely that you'll want to convert argv[0] to an int, as it's the program name, not an argument.

[Shiro]

>I would like to know how do we cast an argv[] if I want to check
>whether it is equal to some integer number or decimal in C ?

Note that argv is the array containing commands on the argument line and the program name. The elements of argv are strings, so I assume you want to convert the strings to int. For that you use atoi().

[Nick]

A char variable can be either unsigned or signed depending on the compiler. So if it's signed the range is
-128 to 127 but if unsigned the range is 0-255.

[Magos]

Originally posted by shaik786
A variable declared as char is capable of storing any integer between the values: -128 to +127

A char is usually defined as unsigned by default, so it's range will be 0-255.

[Nick]

No, a char can be either signed or unsigned. With both compilers I use, gcc and borland, and the char is signed. You can test by running

#include <stdio.h>

int main(void)
{
        char c = 128;
        unsigned char uc = 128;
        signed char sc = 128;

        printf("c = %d\n", c);
        printf("uc = %d\n", uc);
        printf("sc = %d\n", sc);

        return 0;
}

Since just about all machines are 2 complement, if the char is signed then the 128 overflows and you get an output of c = -128.

[Hammer]

K&R says a char being signed or unsigned is machine-dependant. I tend to believe it

[Magos]

Originally posted by Nick
No, a char can be either signed or unsigned. With both compilers I use, gcc and borland, and the char is signed. You can test by running

I know that. I said that a char (notice no prefix) is usually defined as unsigned, if no predefiner is specified. I didn't say that you cannot define signed char's.
Might be me being too unclear in my post though .

[shaik786]

char without any prefix being signed or unsigned will be defined by the compiler. Here, in my compiler, by default it is signed!