基本运算

code

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    int a = 4 + 5 * 2 - 6 / 3 + 11 % 4;
    printf("%d\n", a);
    return 0;
}

获取数值中的每一位

code

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    int a = 4 + 5 * 2 - 6 / 3 + 11 % 4;  /* assign initial value */
    printf("%d\n", a);
    scanf("%d", &a);  /* wait to input when add \n after escape character */
    printf("a = %d\n", a);
    while (a != 0) {
        printf("%d\n", a % 10);
        a /= 10;
    }
    return 0;
}

浮点数运算

存储方式

code

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    float f = 234.56;
    return 0;
}

如何做浮点型的等值运算？

矛盾点—-浮点数无法直接比较大小

code

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    //int a = 8;
    ///* 关系运算符与逻辑运算符搭配 */
    //if (a > 3 && a < 10) {
    //    printf("a is right.\n");
    //}
    //else {
    //    printf("a is wrong.\n");
    //}
    /* 判断两个浮点数是否相等 */
    float f = 234.56;
    if (f == 234.56) {
        printf("f is equal to 234.56.\n");
    }
    else {
        printf("f is not equal to 234.56.\n");
    }
    return 0;
}

解决方案【做差逼近系统设定的精度】

code

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    //int a = 8;
    ///* 关系运算符与逻辑运算符搭配 */
    //if (a > 3 && a < 10) {
    //    printf("a is right.\n");
    //}
    //else {
    //    printf("a is wrong.\n");
    //}
    /* 判断两个浮点数是否相等 */
    float f = 234.56;
    if (f - 234.56 > -0.0001 && f - 234.56 < 0.0001) {
        printf("f is equal to 234.56.\n");
    }
    else {
        printf("f is not equal to 234.56.\n");
    }
    return 0;
}

逻辑非运算符

code1

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    int a = 8;
    /* 关系运算符与逻辑运算符搭配 */
    if (a > 3 && a < 10) {
        printf("a is right.\n");
    }
    else {
        printf("a is wrong.\n");
    }
    /* 判断两个浮点数是否相等 */
    float f = 234.56;
    if (f - 234.56 > -0.0001 && f - 234.56 < 0.0001) {
        printf("f is equal to 234.56.\n");
    }
    else {
        printf("f is not equal to 234.56.\n");
    }
    /* 学习逻辑非 */
    int i = 5, j = 10;
    i = !j;
    printf("i=%d\n", i);
    return 0;
}

code2

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    int a = 8;
    /* 关系运算符与逻辑运算符搭配 */
    if (a > 3 && a < 10) {
        printf("a is right.\n");
    }
    else {
        printf("a is wrong.\n");
    }
    /* 判断两个浮点数是否相等 */
    float f = 234.56;
    if (f - 234.56 > -0.0001 && f - 234.56 < 0.0001) {
        printf("f is equal to 234.56.\n");
    }
    else {
        printf("f is not equal to 234.56.\n");
    }
    /* 学习逻辑非 */
    int i = 5, j = 10;
    i = !!j;
    printf("i=%d\n", i);
    return 0;
}

关于赋值表达式应该注意的

表达式的值只存在于运算过程中

左值只能是变量

自增减运算符巧记

code

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    int i = -1;
    int j;
    /*前++直接按照顺序运算*/
    j = i++ > -1;  /* 拆分成两步：j = i > -1, i++ */
    printf("i = %d, j = %d\n", i, j);
    printf("i 的字节数为: %d.\n", sizeof(i));
    return 0;
}

获取数字输入，输出对应的字符【数字需在0-128之间】

code1

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    char a;
    scanf("%d", &a);
    printf("%c", a);
    return 0;
}

警告

code1

Run-Time Check Failure #2 - Stack around the variable ‘a’ was corrupted.

当你操作的空间，超过了变量本身占用的空间的大小时，就会出现栈崩溃的错误，stack around the variable ‘a’ was corrupted;

code2

#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
int main() {
    int a;
    scanf("%d", &a);
    printf("%c", a);
    return 0;
}