经典编程900例（c语言）（第二十七篇）

例329：时间日期预定义宏

#include <stdio.h>

int main(int argc, char const *argv[])
{
    // 这里的时间编译时已经决定，所以程序每次执行都是一样的
    // __DATE__：编译时刻的日期字符串 如“Jun 17 2017”
    // __TIME__：编译时刻的时间字符串  如”10:00:00“
    printf("Beta Testing: Last compiled %s %s\n", __DATE__, __TIME__);
    return 0;
}

例330：使用宏定义计算两个数最大值和最小值

#include <stdio.h>

// 宏定义（替换）
#define MIN(x, y) (((x) < (y)) ? (x): (y))
#define MAX(x, y) (((x) > (y)) ? (x): (y))

int main(int argc, char const *argv[])
{
    printf("Minimum of 3 and 5 is %d\n", MIN(3, 5));
    printf("Maximum of 3.4 and 3.1 is %f\n", MAX(3.4, 3.1));
    printf("Minimum of -100 and 1000 is %d\n", MIN(-100, 1000));

    return 0;
}

例331：使用宏定义计算两数之和

#include <stdio.h>

#define SUM(x, y) ((x) + (y))

int main(int argc, char const *argv[])
{
    printf("Adding 3 + 5 = %d\n", SUM(3, 5));
    printf("Adding 3.4 + 3.1 = %f\n", SUM(3.4, 3.1));
    printf("Adding -100 + 1000 = %d\n", SUM(-100, 1000));
    
    return 0;
}

例332：使用宏定义计算平方和立方

#include <stdio.h>

#define SQUARE(x) ((x) * (x))
#define CUBE(x) ((x) * (x) * (x))

int main(int argc, char const *argv[])
{
    printf("The square of 2 is %d\n", SQUARE(2));
    printf("The cube of 100 is %f\n", CUBE(100.0));
    
    return 0;
}

例333：字符串的结束

#include <stdio.h>

int main(int argc, char const *argv[])
{
    char string[256];
    int i;

    // 前26个元素用26个字母赋值
    for (i = 0; i < 26; i++)
        string[i] = 'A' + i;

    // 第10个元素赋值位NULL
    string[10] = NULL;

    printf ("The string contains %s\n", string);// The string contains ABCDEFGHIJ
    return 0;
}

例334：字符串转数值1

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char const *argv[])
{
    int int_value;
    float flt_value;
    long long_value;

    //  把字符串转换成整型
    int_value = atoi("12345");
    //  把字符串转换成浮点型
    flt_value = atof("33.45");
    //  把字符串转换成长整型
    long_value = atol("12BAD");

    printf("int %d float %5.2f long %ld\n", int_value, flt_value, long_value);// int 12345 float 33.45 long 12
    
    return 0;
}

例335：字符串转数值2

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char const *argv[])
{
    int int_result;
    float float_result;
    long long_result;

    int_result = atoi("1234");
    float_result = atof("12345.678");
    long_result = atol("1234567L");

    printf("%d %f %ld\n", int_result, float_result, long_result);// 1234 12345.677734 1234567
    
    return 0;
}

例336：字符串的结束2

#include <stdio.h>

int main(int argc, char const *argv[])
{
    char string[256];
    int i;

    for (i = 0; i < 26; i++)
        string[i] = 'A' + i;

    string[i] = NULL;

    printf ("The string contains %s\n", string);// The string contains ABCDEFGHIJKLMNOPQRSTUVWXYZ

    return 0;
}

例337：字符串比较函数

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    // 比较字符串数组的一个方法或函数，但是不可以区分大小写
    printf("Comparing Abc with Abc %d\n", stricmp("Abc", "Abc"));   // Comparing Abc with Abc 0
    printf("Comparing abc with Abc %d\n", stricmp("abc", "Abc"));   // Comparing abc with Abc 0

    // extern int strncmpi(char *str1,char * str2，int n)
    // str1为第一个要比较的字符串，str2为第二个要比较的字符串，n为指定字符串str1和str2进行比较的字符的个数
    printf("Comparing 3 letters abcd with ABC %d\n", strnicmp("abcd", "ABC", 3));   // Comparing 3 letters abcd with ABC 0
    printf("Comparing 5 letters abc with Abcd %d\n", strnicmp("abc", "Abcd", 5));   // Comparing 5 letters abc with Abcd -1

    return 0;
}

例338：字符字面量的双引号表示

#include <stdio.h>

int main(int argc, char const *argv[])
{
    char string[] = "\"Stop!\", he said.";

    printf(string);
    return 0;
}

例339：输出用户输入的字符串和字符个数

#include <stdio.h>

int main(int argc, char const *argv[])
{
    char string[256];
    int i;           

    printf("Type a string of characters and press Enter:\n");
    gets(string);

    // 单个字符打印直到NULL
    for (i = 0; string[i] != NULL; i++)
        putchar(string[i]);

    printf("\nThe number of characters in the string is %d\n", i);
    return 0;
}

例340：字符串函数sprintf()

#include <stdio.h>

int main(int argc, char const *argv[])
{
    int employee_number = 12345;
    char region[] = "SEA";
    char filename[64];

    sprintf(filename, "%s%d", region, employee_number);
    printf("Employee filename: %s\n", filename);
    
    return 0;
}

例341：字符串函数sscanf()

#include <stdio.h>

int main(int argc, char const *argv[])
{
    int age;
    float salary;
    char string[] = "33 25000.00";

    // sscanf读取格式化的字符串中的数据
    sscanf(string, "%d %f\n", &age, &salary);
    printf("Age: %d Salary %f\n", age, salary);// Age: 33 Salary 25000.000000

    return 0;
}