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Overview

The 0x01-variables_if_else_while module covers fundamental programming concepts: declaring variables, making decisions with conditionals, and implementing loops. You’ll learn to control program flow and work with different data types.

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Variables and Random Numbers

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Positive or Negative

This program demonstrates variable declaration, random number generation, and conditional statements.
0-positive_or_negative.c
#include <stdlib.h>
#include <time.h>
#include <stdio.h>
/**
   * main - Entry point
   *Description: This program outputs positive if greater than zero,
   *negative if less than zero, and zero if equal to zero
   *Return: 0 on success
*/
int main(void)
{
int n;

srand(time(0));
n = rand() - RAND_MAX / 2;
if (n > 0)
{
printf("%d is positive\n", n);
}
else if (n < 0)
{
printf("%d is negative\n", n);
}
else
{
printf("%d is zero\n", n);
}
return (0);
}
srand(time(0)) seeds the random number generator with the current time, ensuring different values on each run.
Key concepts:
  • Variable declaration: int n;
  • Random number generation: rand()
  • Conditional logic: if-else if-else

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Conditional Statements

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If-Else Chain

The last digit program shows complex conditional logic:
1-last_digit.c
#include <stdlib.h>
#include <time.h>
#include<stdio.h>
/**
   * main - Entry point
   *Description: This program outputs is greater tahn 5 if greater than five,
   *less than 6 and not if less than 6 and not 0
   *0 if equal to 0
   *Return: 0 on success
*/
int main(void)
{
int n;
int last_digit;

srand(time(0));
n = rand() - RAND_MAX / 2;
last_digit = n % 10;
if (last_digit > 5)
{
printf("Last digit of %d is %d and is greater than 5\n", n, last_digit);
}
else if (last_digit < 6 && last_digit != 0)
{
printf("Last digit of %d is %d and is less than 6 and not 0\n", n, last_digit);
}
else if (last_digit == 0)
{
printf("Last digit of %d is %d and is 0\n", n, last_digit);
}
return (0);
}
The modulo operator % gets the remainder. n % 10 extracts the last digit of any number.
  • && : Logical AND (both conditions must be true)
  • || : Logical OR (at least one condition must be true)
  • ! : Logical NOT (negates the condition)
  • == : Equality comparison
  • != : Not equal comparison

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Loops

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For Loop - Printing the Alphabet

2-print_alphabet.c
#include <stdio.h>
/**
   * main - Entry point
   *Description: This program prints the alphabet in lowercase
   *Return: 0 on success
*/

int main(void)
{
char alphabet;
for (alphabet = 'a'; alphabet <= 'z' ; alphabet++)
putchar(alphabet);
putchar('\n');
return (0);
}
For loop structure:
  1. Initialization: alphabet = 'a' - sets starting value
  2. Condition: alphabet <= 'z' - continues while true
  3. Increment: alphabet++ - executes after each iteration
In C, characters are actually integers (ASCII values). You can increment them: 'a' becomes 'b', etc.

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For Loop - Printing Numbers

5-print_numbers.c
#include <stdio.h>
/**
 * main - Entry point
 *Description: This program prints all single digit numbers
 *of base 10 starting from 0
 *Return: 0 on success
 */

int main(void)
{
int number;
for (number = 0; number <= 9; number++)
{
printf("%d", number);
}
printf("\n");
return (0);
}

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While Loop - Combinations

9-print_comb.c
#include <stdio.h>
/**
 * main - Entry point
 * Description: Write a program that prints all possible combinations
 * of single-digit numbers.
 * Return: 0 on success
 */

int main(void)
{
int number = 0;

while (number < 10)
{
putchar('0' + number);
if (number != 9)
{
putchar(',');
putchar(' ');
}
number++;
}
putchar('\n');
return (0);
}
'0' + number converts an integer to its character representation. '0' + 5 gives '5'.

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Loop Types Comparison

Best when you know how many iterations you need.
for (i = 0; i < 10; i++)
{
    /* code */
}

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putchar() vs printf()

Both functions output characters, but with different use cases: 
/* Outputs a single character */
putchar('A');
putchar('\n');
putchar() is more efficient for single characters. Use printf() when you need formatting or multiple values.

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Common Patterns

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Printing with Separators

A common pattern is printing items with commas between them (but not after the last item): 
for (i = 0; i < 10; i++)
{
    printf("%d", i);
    if (i != 9)  /* Not the last item */
        printf(", ");
}

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Infinite Loop Prevention

Always ensure your loop condition will eventually become false:Bad:
int i = 0;
while (i < 10)
{
    printf("%d", i);
    /* Forgot to increment i! */
}
Good:
int i = 0;
while (i < 10)
{
    printf("%d", i);
    i++;  /* Loop will terminate */
}

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Compilation and Testing

# Compile with all warnings
gcc -Wall -Werror -Wextra -pedantic -std=gnu89 0-positive_or_negative.c -o positive

# Run multiple times to see different random values
./positive
./positive
./positive

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Best Practices

Initialize variables before useAlways initialize variables to avoid undefined behavior:
int number = 0;  /* Good */
int other;       /* Contains garbage value */
Use meaningful variable nameslast_digit is clearer than ld or x. Code readability matters!
Proper indentationIndent code blocks consistently (Betty style uses tabs). It makes logic easier to follow.

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Common Pitfalls

Wrong:
if (n = 0)  /* This assigns 0 to n! */
Correct:
if (n == 0)  /* This compares n to 0 */
  • Single quotes for characters: 'a'
  • Double quotes for strings: "hello"
putchar('a');      /* Correct */
putchar("a");      /* Wrong - type mismatch */

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