19级图灵班第一节课

19图灵班

这节课安排

• think C里面的内容
  
  • hello_world.c
  • variable.c
  • read_from_input.c
  • array_loop.c
  • example.c
  • new_func.c
• 做几道简单题目
  
  • 阶乘、连乘

有空的话

• Think C解答和知识点强化

源代码

hello_world.c

// hello_world.c
#include <stdio.h>
#include <stdlib.h>
int main() {
    printf("Hello World\n");
    return 0;
}

variable.c

#include <stdio.h>
int main() {
    // Define a variable `a`
    int a;
    // Assign `a` with 1
    a = 1;
    // Initialization variable `b`
    // Which means that declare and assign
    int b = 2;
    printf("a = %d\nb = %d\n", a, b);
    // We can define many variables at a time
    int a1, a2, a3, a4;
    // Integer
    // 2 bytes
    short s = 1;
    int i = 1;
    long int i1 = 1;
    long long i2 = 1;
    unsigned int u3 = -1;
    printf("u3 = %lu\n", u3);
    // Floating point
    float f = 1.0;
    double d = 3.14;
    printf("f = %f, d = %lf\n", f, d);
    // Character in ASCII
    char c = 'a';
    printf("char c = %c\n", c);
    return 0;
}

read_from_input.c

#include <stdio.h>
// For more placeholder, please consult
// https://en.cppreference.com/w/c/io/fprintf
int main() {
    // Sometimes we need to know a number/string/... from user
    // Put a `&` before variable `a`
    // `%d` in `""` is a place holder for variables
    int d, a;
    scanf("%d%d", &d, &a);
    printf("%d %d\n", a, d);
    char c = 'a';
    printf("char = %c, f = %f, d = %lf", c, 3.14, 1.0);
    return 0;
}

array_loop.c

#include <stdio.h>
#include <stdlib.h>
int main() {
    // We have got one variable `a`
    int a = 1;
    printf("%d", a);
    // We can define many variables at a time
    int a1, a2, a3, a4;
    // What if we need no more than one?
    // Like 100 int variables?
    int arr[10];
    int arr1[] = {1, 2, 3, 4, 5, 6};
    // As we get array now, how do we use it?
    // What we need is loop
    // array could be used from subscript `0`
    // `i++` equivalent to `i = i +1` and `i += 1`
    int n = 0;
    while (n < 10) {
        printf("%d,", arr[n]);
        n += 1;
    }
    printf("\n");
    // Control flow:
    // 1. Initialization: `int i = 0;`
    // 2. Test condition: `i < 6`, go to 6 if predicate does not fulfill
    // 3. {} body
    // 4. Incresment of i: `i++`
    // 5. Go to 2
    // 6. Done
    for (int i = 0; i < 6; i++) {
        printf("%d,", arr1[i]);
    }
    printf("\n");
    // Do-while guarantee it will be do at least one time.
    int i = 0;
    int arr2[4] = {};
    do {
        printf("%d,", arr2[i++]);
    } while (i < 4);
    return 0;
}

example.c

#include <stdio.h>
int main() {
    printf("Enter the amount of student number:");
    int num;
    scanf("%d", &num);
    int arr[num];
    for (int i = 0; i < num; i++) {
        printf("Enter %d th studen's score:", i);
        scanf("%d", &arr[i]);
    }
    // Code below is equivalent to code above
    // int i = 0;
    // while (i < num) {
    //    printf("Enter %d th studen's score:", i);
    //    scanf("%d", &arr[i]);
    //    i++;
    //}
    int i = 0;
    while (i < num) {
        printf("The %d th student's score is %d\n", i, arr[i]);
        i++;
    }
    return 0;
}

new_func.c

#include <stdio.h>
/*
 * Two ways to declare new function
 * 1. Declare before use, then implement it after. In this case: bar()
 * 2. Define before use. In this case: foo()
 */
void bar();
void foo() {
    printf("Hello ");
    printf("World\n");
}
int main() {
    foo();
    bar();
    return 0;
}
void bar() {
    printf("Hello ");
    printf("Class");
}

sum_and_fac.c

#include <stdio.h>
int sum(int num) {
    int sum = 0;
    for (int i = 1; i <= num; i++) {
        sum = sum + i;
    }
    return sum;
}
int factorial(int n) {
    if (n < 0) {
        return 0;
    }
    if (n == 0) {
        return 1;
    } else {
        return factorial(n - 1) * n;
    }
}
int main() {
    int num;
    scanf("%d", &num);
    printf("sum of 1 to %d is %d\n", num, sum(num));
    printf("factorial of %d is %d\n", num, factorial(num));
    return 0;
}