Printing an integer entered by the user is one of the most fundamental tasks in C programming. This article explores various methods to achieve this with different examples and solutions, highlighting the versatility of C language. Each example will be explained, including its prerequisites and output.
Prerequisites
Before diving into the examples, ensure you have the following:
- Basic understanding of C programming.
- Knowledge of basic input and output functions in C (
printfandscanf).
1. Basic Program to Print an Integer
1.1 Explanation
This is the simplest form of a C program where the user is prompted to enter an integer, and the program prints the entered integer.
1.2 Program: Basic Integer Input and Output
#include <stdio.h>
int main() {
int num;
// Prompt the user for an integer input
printf("Enter an integer: ");
scanf("%d", &num);
// Output the entered integer
printf("You entered: %d\n", num);
return 0;
}
1.3 Output
Enter an integer: 42
You entered: 42
2. Program with Input Validation
2.1 Explanation
In this example, we add a basic form of input validation to ensure that the user enters a valid integer.
2.2 Program: Input Validation
#include <stdio.h>
int main() {
int num;
// Prompt the user for an integer input
printf("Enter an integer: ");
if (scanf("%d", &num) != 1) {
printf("Invalid input. Please enter an integer.\n");
return 1;
}
// Output the entered integer
printf("You entered: %d\n", num);
return 0;
}
2.3 Output
Enter an integer: abc
Invalid input. Please enter an integer.
3. Program with Range Check
3.1 Explanation
This example ensures the entered integer falls within a specified range.
3.2 Program: Range Check
#include <stdio.h>
int main() {
int num;
// Prompt the user for an integer input
printf("Enter an integer between 1 and 100: ");
if (scanf("%d", &num) != 1 || num < 1 || num > 100) {
printf("Invalid input. Please enter an integer between 1 and 100.\n");
return 1;
}
// Output the entered integer
printf("You entered: %d\n", num);
return 0;
}
3.3 Output
Enter an integer between 1 and 100: 150
Invalid input. Please enter an integer between 1 and 100.
4. Program with Command-Line Arguments
4.1 Explanation
This example demonstrates how to use command-line arguments to input an integer.
4.2 Program: Command-Line Arguments
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[]) {
int num;
// Check if the correct number of arguments is provided
if (argc != 2) {
printf("Usage: %s <integer>\n", argv[0]);
return 1;
}
// Convert command-line argument to integer
num = atoi(argv[1]);
// Output the entered integer
printf("You entered: %d\n", num);
return 0;
}
4.3 Output
$ ./program 42
You entered: 42
5. Program with Error Handling for Command-Line Arguments
5.1 Explanation
This example includes error handling for non-integer command-line arguments.
5.2 Program: Error Handling for Command-Line Arguments
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int is_number(const char *str) {
while (*str) {
if (!isdigit(*str)) return 0;
str++;
}
return 1;
}
int main(int argc, char *argv[]) {
int num;
// Check if the correct number of arguments is provided
if (argc != 2) {
printf("Usage: %s <integer>\n", argv[0]);
return 1;
}
// Validate that the argument is a number
if (!is_number(argv[1])) {
printf("Invalid input. Please enter a valid integer.\n");
return 1;
}
// Convert command-line argument to integer
num = atoi(argv[1]);
// Output the entered integer
printf("You entered: %d\n", num);
return 0;
}
5.3 Output
$ ./program abc
Invalid input. Please enter a valid integer.
Conclusion
This comprehensive guide explored multiple methods to print an integer entered by the user in C. From basic input/output operations to adding input validation, range checks, and using command-line arguments, each method offers a unique approach to handling user input. Understanding these variations will help you develop more robust and user-friendly C programs.