写出五个简单的c语言程序

当然可以。以下是五个简单的 C 语言程序示例，包括打印 "Hello, World!"、计算两个数之和、交换两个变量值、检查字符是否为数字以及输入字符串并求长度：

1. **Hello, World!** (最简单的程序)

#include <stdio.h>
int main() {
   printf("Hello, World!\n");
   return 0;
}

2. **加法计算器**

#include <stdio.h>
int main() {
   int num1, num2, sum;
   printf("Enter two numbers: ");
   scanf("%d %d", &num1, &num2);
   sum = num1 + num2;
   printf("Sum: %d\n", sum);
   return 0;
}

3. **交换两个变量**

#include <stdio.h>
void swap(int* a, int* b) {
   int temp = *a;
   *a = *b;
   *b = temp;
}
int main() {
   int x = 5, y = 10;
   printf("Before swap: x=%d, y=%d\n", x, y);
   swap(&x, &y);
   printf("After swap: x=%d, y=%d\n", x, y);
   return 0;
}

4. **判断字符是否为数字**

#include <stdio.h>
char is_digit(char c) {
   if(c >= '0' && c <= '9') {
      return 1; // 返回非零值表示是数字
   } else {
      return 0;
   }
}
int main() {
   char ch;
   printf("Enter a character: ");
   scanf(" %c", &ch);
   if(is_digit(ch)) {
      printf("%c is a digit.\n", ch);
   } else {
      printf("%c is not a digit.\n", ch);
   }
   return 0;
}

5. **读取字符串并求长度**

#include <stdio.h>
#include <string.h>
int main() {
   char str[100];
   printf("Enter a string: ");
   fgets(str, sizeof(str), stdin);
   str[strcspn(str, "\n")] = '\0'; // 清除换行符
   int len = strlen(str);
   printf("Length of the string: %d\n", len);
   return 0;
}