is there a function in c that checks if n is a number code example

Example 1: check command line input is a number in c

bool isNumber(char number[])
{
    int i = 0;

    //checking for negative numbers
    if (number[0] == '-')
        i = 1;
    for (; number[i] != 0; i++)
    {
        //if (number[i] > '9' || number[i] < '0')
        if (!isdigit(number[i]))
            return false;
    }
    return true;
}

Example 2: how to know if a number is even in c

if((x & 1) == 0)
    printf("EVEN!\n");
else
    printf("ODD!\n");