1. 交换两个数的值：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {int a = 5, b = 10, c = 0;c = a;a = b;b = c;printf("a=%d b=%d", a, b);
}

2. 键盘录入一个数组判断数组最大值：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {int max = 0;int arr[10] = { 0 };for (int i = 0; i < 10; i++) {printf("请输入第%d个数：",i+1); //从0开始所以为i+1scanf("%d", &arr[i]);       if (arr[i] > max) {max = arr[i];}}printf("最大值为%d", max);
}

3. 判断闰年：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {int year;printf("请输入一个年份：");scanf("%d", &year);if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {//判断闰年条件printf("yes");}else {printf("no");}
}

4. 判断大小写字母数组，特殊符号：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {char num;printf("输入一个字符数字或特殊符号：");scanf("%c", &num);if (num >= 'a' && num <= 'z') {printf("是小写字母。");}else if (num >= 'A' && num <= 'Z') {printf("是大写字母。");}else if (num >= '0' && num <='9') {printf("是数字。");}else {printf("是特殊符号。");}
}

5.输入小写字母转大写字母，输入大写字母转小写字母：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {char ch;printf("请输入你要转换的字母：");scanf("%c", &ch);if (ch >= 'a' && ch <= 'z') {ch = ch - 32;}else if(ch >= 'A' && ch <= 'Z'){ch = ch + 32;}else {printf("输入不合法.");}printf("%c", ch);
}

6. 打印三角形：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {for (int i = 0; i <= 6; i++) {for (int j = i; j <= 5; j++) {printf("*");}printf("\n");}
}

  

7. 打印正三角：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {for (int i = 0; i <= 6; i++) {for (int j = 0; j <= i; j++) {printf("*");}printf("\n");}
}

  

8. 打印九九乘法表：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {for (int i = 1; i <= 6; i++) {for (int j = 1; j <= i; j++) {printf("%d*%d=%2d ",j,i,j*i);}printf("\n");}
}

9. 冒泡排序法：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int main() {int arr[10];int t = 0;for (int i = 0; i < 10; i++) {printf("请输入第%d个数：", i + 1);scanf("%d", &arr[i]);}for (int i = 0; i < 10; i++) {/*printf("请输入第%d个数：", i + 1);scanf("%d", &arr[i]);*/for (int j = 0; j < 10 - 1 - i; j++) {    if (arr[j + 1] > arr[j]) {    //从大到小，arr[j]>arr[j+1]为从小到大t = arr[j];arr[j] = arr[j + 1];arr[1+ j] = t;}}}for (int i = 0; i < 10; i++) {printf("%d\t",arr[i]);}}

10.累加函数：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
double sum(int kai, int jie) {int sum = 0;for (int i = kai; i <= jie; i++) {sum = sum + i;}return sum;
}
int main() {double num = sum(1, 100);printf("和为%5.2f", num);
}

11. 函数输入三个数，输出最大值：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
double max(int a, int b, int c) {int arr[3] = { a,b,c };int max = 0;for (int i = 0; i < 3; i++) {if (arr[i] > max){max = arr[i];}}return max;}
int main() {double number = max(1, 100,2);printf("最大值为%4.2f", number);

12.函数给出两个数和符号，给出计算结果：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int math(int a, int b, char c) {int num;if (c == '+') {num = a + b;}else if (c == '-') {num = a - b;}else if (c == '*') {num = a * b;}else if (c == '/') {num = a / b;}else if (c == '%') {num = a % b;}else {num = printf("输入不合法");}
}
int main() {int number = math(23,2,'/');printf("计算结果为%d", number);
}

 13. 函数求一个数组的和：

#include <stdio.h>
#define CRT_SECURE_NO_WARNINGS
int add(int a[],int length) {int sum=0;for (int i = 0; i < length; i++) {sum = sum + a[i];}return sum;
}
int main() {int a[9] = { 23,34,12,45,12,345,45,67,23 };int sum = add(a, 9);printf("数组和为%d", sum);
}