C语言控制语句：类型、示例与用法

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if (condition) {
    // 条件为真时执行的语句
} else {
    // 条件为假时执行的语句
}

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#include<stdio.h>
int main() {
  int a;
  printf("\n Enter a number:");
  scanf("%d", &a);

  if(a>0) { 
    printf("\n The number %d is positive.",a);
  } else {
    printf("\n The number %d is negative.",a);
  }
  return 0;
}

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#include <string.h>

int main() {
    char a[20], b[20];

    printf("\n Enter the first string:");
    scanf("%s",a);
    printf("\n Enter the second string:");
    scanf("%s",b);

    if((strcmp(a,b)==0)) {
        printf("\nStrings are the same");
    } else {
        printf("\nStrings are different");
    }

    return 0;
}

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int strcmp(const char *s1, const char *s2);

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if(condition1) {
    // condition1为真时的语句
} else if(condition2) {
    // condition2为真时的语句
} else if(conditionN) {
    // conditionN为真时的语句
} else {
    // 所有条件都不为真时的语句
}

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#include<stdio.h>
int main() {
    int a = 6, b = 5, c = 10;

    if(a > b) {
        if(a > c) {
            printf("\nGreatest is: %d", a);
        } else {
            printf("\nGreatest is: %d", c);
        }
    } else if(b > c) {
        printf("\nGreatest is: %d", b);
    } else {
        printf("\nGreatest is: %d", c);
    }
    return 0;
}

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switch (expression) {
  case value1:
    // 代码段1
    break;
  case value2:
    // 代码段2;
    break;
  ...
  case valueN:
    // 代码段N
    break;
  default:
    // 默认代码段
}

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#include<stdio.h>

int main() {
  int day;
  printf("\nEnter the number of the day:");
  scanf("%d",&day);

  switch(day) {
      case 1:
        printf("Sunday");
        break;
      case 2:
        printf("Monday");
        break;
      case 3:
        printf("Tuesday");
        break;
      case 4:
        printf("Wednesday");
        break;
      case 5:
        printf("Thursday");
        break;
      case 6:
        printf("Friday");
        break;
      case 7:
        printf("Saturday");
        break;
      default:
        printf("Invalid choice");
  }
  return 0;
}

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#include<stdio.h>

int main() {
  int choice;
  printf("\nPlease select from the following options:");
  printf("\n1. Add a record at the end of the file.");
  printf("\n2. Add a record at the beginning of the file.");
  printf("\n3. Add a record after a particular record.");
  printf("\nPlease enter your choice (1/2/3): ");
  scanf("%d", &choice);

  switch(choice) {
      case 1:
        // 在文件末尾添加记录的代码
        break;
      case 2:
        // 在文件开头添加记录的代码
        break;
      case 3:
        // 在特定记录后添加记录的代码
        break;
      default:
        printf("\nWrong Choice");
  }
  return 0;
}

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for(initialization; termination; increment/decrement) { 
    //要执行的语句 
}

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#include<stdio.h>
int main() {
  int i, n, a = 0, b = 1, sum;
  printf("Enter the number of terms: ");
  scanf("%d", &n);

  printf("%d %d", a, b);

  for(i = 2; i < n; i++) {
    sum = a + b;
    printf(" %d", sum);
    a = b;
    b = sum;
  }

  return 0; 
}

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int i = 0; // 循环前初始化
for(; i < 5; i++) {
    printf("%d ", i);
}

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for(int i = 0; ; i++) {
    if(i == 5) break; // 在循环内指定条件
    printf("%d ", i);
}

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#include<stdio.h> 
int main() {
  int i,n, a, b, sum=0;
  printf("Enter the number of terms:");
  scanf("%d",&n); 
  a=0;
  b=1;
  printf("%d\n %d", a, b);

  for(i=2; ;i++) {
    if(i==(n-1)) { //使用if语句指定条件
      break;
    }
    
    sum=a+b;
    printf("\n%d",sum);
    a=b;
    b=sum;
  }

  return 0;
}

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for(int i = 0; i < 5;) {
    printf("%d ", i);
    i++; // 循环体内递增
}

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for(;;) {
  //语句 
}

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while (condition) {
  //要执行的语句 
}

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#include<stdio.h>
int main() {
  int n, a, sum = 0;
  printf("\nEnter a number: ");
  scanf("%d", &n);

  while(n > 0) {
    a = n % 10; // 提取最后一位数字
    sum = sum + a; // 加到总和中
    n = n / 10; // 移除最后一位数字
  }

  printf("\nSum of the digits = %d", sum);
  return 0; 
}

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#include<stdio.h>
int main() {
  int n, m, a, reverse = 0;
  printf("\nEnter a number: ");
  scanf("%d", &n);
  m = n;

  while(n > 0) {
    a = n % 10; // 提取最后一位数字
    reverse = reverse * 10 + a; // 构建反转数字
    n = n / 10; // 移除最后一位数字
  }

  if (m == reverse) {
    printf("\nThe number is a palindrome.");
  } else {
    printf("\nThe number is not a palindrome.");
  }
  return 0;
}

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do { 
  //要执行的语句;  
} 
while(condition);