将字符数字转换成double型数字

//linux下int str_to_num(char *string){int num=0;int i=0;for(i=0;i<strlen(string);i++){switch(string[i]){case '0':num=num*10+0;break;case '1':num=num*10+1;break;case '2':num=num*10+2;break;case '3':num=num*10+3;break;case '4':num=num*10+4;break;case '5':num=num*10+5;break;case '6':num=num*10+6;break;case '7':num=num*10+7;break;case '8':num=num*10+8;break;case '9':num=num*10+9;break;case ' ':break;case '\t':break;default:printf("ERROR:unrecongnized letter in funciong str_to_num\n");exit(0);break;}}return num;}