C考试几个编程题总结

1.把一个字符串转化为整数：比如“12345”->12345

#include <stdio.h>
#include <windows.h>
#define MAX_INT 0x7FFFFFFF
#define MIN_INT 0x80000000

typedef enum status{
VALID=0,//合法
INVALID,//非法
}status_t;

int str_to_int_core(char *int_str, status_t *s, int symbol)//判断输入的字符是否合法,是则转
{
long long num = 0;
while (*int_str != '\0'){
if (*int_str >= '0' && *int_str <= '9'){
num = num * 10 + symbol*(*int_str - '0');
}
else{
*s = INVALID;
return 2;
}
int_str++;
}
if ( (symbol == 1 && num > MAX_INT) || \
(symbol == -1 && num < (signed int)MIN_INT))//输入的字符虽然合法，但要判断int能否装下
{
printf("num is overflow!\n");
*s = INVALID;
return 3;
}
return (int)num;
}
int str_to_int(char *int_str, status_t *s)
{
*s = VALID;
if (NULL == int_str || *int_str == '\0' || NULL == s){
*s = INVALID;
return 1;
}
int symbol = 1;
if (*int_str == '+'){
int_str++;
}
else if (*int_str == '-'){
symbol = -1;
int_str++;
}
else{
//DO NOTHING
}
return str_to_int_core(int_str, s, symbol);

}

int main()
{
char int_str[] = "-123456";
status_t s;
int ret_int = str_to_int(int_str, &s);
if (s == VALID){
printf("result int : %d\n", ret_int);
}
else{
printf("errno code : %d\n", ret_int);
}
system("pause");
return 0;
}

2.把一个二进制数的一位置1或置0，其它为保持不变

#include <stdio.h>
#include <windows.h>
void show_bit(unsigned char bit_8)
{
int i = 0;
unsigned char flag = 0x80; //1000 0000
for (; i < sizeof(unsigned char)* 8; i++){
if (flag & bit_8){
printf("1");
}
else{
printf("0");
}
flag >>= 1;
}
printf("\n");
}

#define _ZERO_ 0//for flag
#define _ONE_  1
void bit_set(unsigned char *p_data, unsigned char pos, int flag)
{
if (flag == _ZERO_)
{
*p_data &= ~(0x1 << pos);
}
else if (flag == _ONE_)
{
*p_data |= (0x1 << pos);
}
else
{
return;
}
}

int main()
{
unsigned char tmp = 0x0f;
show_bit(tmp);
bit_set(&tmp, 7, _ONE_);
show_bit(tmp);
bit_set(&tmp, 0, _ZERO_);
show_bit(tmp);
system("pause");
return 0;
}