The C Programming Language Chapter-1

Chapter-1 A Tutorial Introduction

Notes of The C programming Language

Integer Division of C

In C, integer division will truncate the result to zero, regardless of whether the result is positive or negative.

printf Conversion Specification %f

For example, %6.4f means printf should print the value as floating point, at least 6 characters wide (it means the total width) and 4 after the decimal point.

#include <stdio.h>

int main() {
    float printFloatWidth1 = 1111.222;
    float printFloatWidth2 = 0.2;
    printf("printFloatWidth1: %6.4f\n", printFloatWidth1);
    printf("printFloatWidth2: %6.2f\n", printFloatWidth2);
    return 0;
}

printFloatWidth1: 1111.2220
printFloatWidth2:   0.20

If the valid digits of the value cannot fill the least width, printf will fill it with spaces, as illustrated in printFloatWidth2.

Symbolic Constants

#define PI 3.1415

Input and Output

C provides getchar() and putchar() as the user input/output interface. Comparing with InputStream and OutputStream in Java, input and output methods in C do not specify the source, destination and whether use buffer explicitly. getchar() and putchar() implicitly set console as input source and output destination, and enable buffer.

It’s worth noting that \n is not EOF. When we enter \n in the terminal, the program will push the buffer (including \n itself) to the while loop including getchar(). Then getchar() will read every character till the buffer is empty, and getchar() will block on it. Although the behaviors of this ‘echo’ program like it’s processing strings, it can only recognize characters one by one.

A simple example

void copyInput() {
    int c;
    while ((c=getchar())!=EOF) {
        putchar(c);
    }
}

1
1
14515
14515
6236534
6236534
   151
   151

Declare functions in a compatible format

We all know if you leave empty in the definition of C function argument list, it means this function need no argument. But for the compatibility with older C programs, it would be better to use void for an explicitly empty argument list.

#include <stdio.h>

int getLine(void);
int copy(void);

int main() {
    return 0;
}