Control Flow: Number Classifier

CSC-115 · Semester I · C Programming

beginner25 minAvailable

Cin-browser interpreter · runs locally

#include <stdio.h>

int main() {
  int n;
  printf("Enter an integer: ");
  scanf("%d", &n);

  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;
}

17 lines

Output

Write some code, then press Run. Stdout and errors appear here.

Lab brief

Objective

Use if-else branching and arithmetic operators in C to classify an integer as positive, negative or zero, and to test divisibility.

Theory & concepts

A number classifier chains decisions: first check the sign, then test for special properties such as being even or divisible by another number. In C each decision is made with an if-else statement and a boolean expression built from relational and logical operators.

Rendering diagram…

Decision tree of the number classifier

int n;
scanf("%d", &n);

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);
}

if (n % 2 == 0)
    printf("%d is even\n", n);
else
    printf("%d is odd\n", n);

Notice how else if ties several mutually exclusive cases together, and how the modulo operator % tests divisibility by checking that the remainder is zero. Only one branch of the if-else chain ever runs.

Prerequisites

Lesson: Operators and expressions
Lesson: Decision making: if, if-else and switch

Instructions

1Read one integer from standard input.
2Classify it as positive, negative or zero with an if-else chain.
3Add a check for even/odd using the modulo operator.
4Test with positive, negative and zero inputs.
5Extend the program to also test divisibility by 3.

Tasks

Sign classification
Print 'positive', 'negative' or 'zero' for the input.
Even or odd
Print whether the number is even or odd.
Divisibility
Print whether the number is divisible by 3.
Verify edge cases
Run with -7, 0 and 12 and confirm the output.

Self-check

The if-else chain runs exactly one branch for each input.
Even/odd and divisibility results match hand computation.
The program compiles and runs without warnings.

Environment

editorstandard inputstdout consoletest cases