how to check if input is integer in c code example

Example 1: how to make sure input is integer c

#include <string.h>  

bool isNumber(string s) 
{ 
    for (int i = 0; i < strlen(s); i++) 
        if (isdigit(s[i]) == false) 
            return false; 
  
    return true; 
}

Example 2: c check if argument is integer

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;
}