how to check if a string is a number C code example

Example 1: c string is int

int isNumber(char s[])
{
    for (int i = 0; s[i]!= '\0'; i++)
    {
        if (isdigit(s[i]) == 0)
              return 0;
    }
    return 1;
}

Example 2: check if string in string c

if(strstr(sent, word) != NULL) {
    /* ... */
}

Example 3: how to know if a number is even in c

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