反转字符串

char *reverse(char * s){

if(s==NULL) return NULL;

int n = strlen(s);

int m = n/2;

char tmp;

for(int i=0;i<m;i++){

tmp = s[i];

s[i] = s[n-i-1];

s[n-i-1] = tmp;

}

return s;

}