第17行“cS[iI]!='\0'"里边那个感叹号是啥意思，为啥要加他

#include<stdio.h>
int main()
{
    char cS[100];
    int iI,iW=1;
    char cBlank;
    gets(cS);
    if(cS[0]=='\0')
    {
        printf("There is no char!\n");
    }
    else if(cS[0]==' ')
    {
        printf("First char just is a blank!\n");
    }
    else
    {
        for(iI=0;cS[iI]!='\0';iI++)      \*第17行*\
        {
            cBlank=cS[iI];
            if(cBlank==' ')
            {
                iW++;
            }
        }
        printf("%d\n",iW);
    }
    return 0;
}