一种解法非常好：状态机。在各种状态之间跳转，逻辑清晰，不易出错，出错了也容易调试。

下面把代码贴出来：

    #include <stdio.h>                int state;                int c1,c2;                void change_state(int c);                int main(int argc, const char * argv[]) {            int c;            state = 0;            c1 = 0;            c2 = 0;            while ((c=getchar())!=EOF) {                c1 = c2;                c2 = c;                change_state(c);            }            if (/* DISABLES CODE */ (0)==1) {                printf("just test://abcd");                printf("just test:/*hello*/");            }        }                /*状态机函数*/        void change_state(int c){            if (state==0) {//普通状态                if (c=='/') {                    state = 1;                }else if (c=='"'){                    state = 5;                    putchar(c);                }else if (c=='\''){                    state = 6;                    putchar(c);                }                else{                    state = 0;                    putchar(c);                }            }else if (state==1) {//检测到1个'/'                if (c=='/') {                    state = 2;                }else if (c=='*'){                    state = 3;                }else{                    state = 0;                    putchar(c1);                    putchar(c);                }            }else if (state==2) {// "//"注释状态                if (c=='\n') {                    state = 0;                    putchar(c);                }else{                    state = 2;                }            }else if (state==3) {// "/*"注释状态                if (c=='*') {                    state = 4;                }else{                    state = 3;                }            }else if (state==4) {                if (c=='/') {                    state = 0;                }else{                    state = 3;                }            }else if (state==5){//在"字符串里                if (c=='"') {                    state = 0;                    putchar(c);                }else if(c=='\\'){                    state = 7;                    putchar(c);                }else{                    state = 5;                    putchar(c);                }            }else if (state==6){//在'字符里                if (c=='\'') {                    state = 0;                    putchar(c);                }else if(c=='\\'){                    state = 8;                    putchar(c);                }else{                    state = 6;                    putchar(c);                }            }else if (state==7){//在"字符串里的"\"                state = 5;                putchar(c);            }else if (state==8){//在'字符串里的"\"                state = 6;                putchar(c);            }        }