Basics

Last updated on Feb 1, 2024

Coursera, C programming for everyone. cc4e.com/book/chap01.md

`scanf`

This reads the input and converts accordingly to the variables.

#include <stdio.h>
int main() {
    int usf, euf;
    printf("Enter US Floor\n");
    scanf("%d\n", &usf);
    euf = usf - 1;
    printf("EU Floor %d\n", euf);
}

This can also be used to read in new lines. Inside the brackets are the regular expressions. Everything before a new line character.

#include <stdio.h>

int main() {
    char line[1024];  // Assuming a maximum input line length of 1024 characters

    printf("Enter line\n");
    scanf("%[^\n]", line);  // Reads until a newline is encountered
    printf("Line: %s\n", line);

    return 0;
}

`fgets()`

An alternative way to use fgets().

stdin is the predefined constant. This is the file handle.

#include <stdio.h>

int main() {
    char line[1024];  // Assuming a maximum input line length of 1024 characters

    printf("Enter line\n");
    fgets(line, sizeof(line), stdin);  // Reads a line from standard input
    printf("Line: %s\n", line);

    return 0;
}

Some other functions…

gets() receives whatever input excluding the \n char, that’s why we can compare it to "done".
strcmp returns any numbers. When two strings are equal, it returns 0, and unpredictable sign when they are unequal.
atoi requires the #include <stdlib.h>. This converts a string of integer to integer.
We need !=NULL because when gets() encounters EOF or an error, a NULL will be returned

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    int first = 1;
    int val, maxval = 0, minval = 0;  // Initialize maxval and minval
    char rawInput[1000];  // Increased buffer size

    while(gets(rawInput) != NULL) {
        if (strcmp(rawInput, "done") == 0) {
            break;
        }

        val = atoi(rawInput);

        if (first) {
            maxval = val;
            minval = val;
            first = 0;
        } else {
            if (val > maxval) maxval = val;
            if (val < minval) minval = val;
        }
    }
    
    if (!first) {  // Check if at least one number was entered
        printf("Maximum %d\n", maxval);
        printf("Minimum %d\n", minval);
    } else {
        printf("No numbers entered.\n");
    }
    
    return 0;
}

Termination of Input

The termination can be controlled by the EOF constant. On Windows, for example, If we press ctrl + Z and then press Enter, the program will be terminated.

#include "stdio.h"

int main() {
    float total, input;
    int n, result;
    while (1) {
        result = scanf("%f", &input);
        if (result == EOF) {
            printf("User Terminated");
            break;
        }
        printf("You Entered %f\n", input);
    }
    return 0;
}

Reading Files

Omitted.

Functions

int mymult(int a, int b) {
    int c = a * b;
    return c;
}

Even if we don’t declare the int for a and b. There will be no bug because for unspecified types, int will be applied.

String

No string in C, just array of characters marked by a zero as the termination.

"" and '' are very different things, as "" means the string array, only single quote is the char.

Example: remove the extra spaces

#include <stdio.h>

int main() {
    int c, prevc;
    prevc = EOF;  // Initialize prevc to EOF

    while ((c = getchar()) != EOF) {
        if (c == ' ' && prevc == ' ') {
            continue;  // Skip the loop iteration if the current and previous characters are spaces
        }
        putchar(c);  // Output the current character
        prevc = c;   // Update prevc to the current character
    } 

    return 0;
}

Types, Operators, Expressions

int i,j; i = 42; j = i++; assignment happens first and then the increment happens
Use [condition] ? [if true] : [if false] to replace the if and else.