Num1: //用指针
int strlen(char *p){char *q = p;while(*q != ' ') q++;retrun q - p;}Num2: // 用指针
int strlen(char *p){int num;for(num = 0; *p != ' '; p++) num++;return num;}Num3: //用数组方法，效率相对偏低
int strlen(char p[]){int i = 0;while(p[i] != ' ') i++;return i;}