C - User Input: Handling Data from Users

User input is a crucial aspect of computer applications, enabling data collection for processing and output. In C, while there are no dedicated keywords for reading user inputs, the scanf() function from the stdio.h library is commonly employed to capture data. This section explores how to effectively implement user input in C programs.

C - User Input

Every computer application accepts data from the user, processes it, and produces output. There are no keywords in C to read user inputs. Instead, the stdio.h library function scanf() is commonly used for this purpose.

Example: User Input in C

Code Snippet: C


#include 

int main() {
    int price, qty, ttl;

    printf("Enter price and quantity: ");
    scanf("%d %d", &price, &qty);

    ttl = price * qty;

    printf("Total: %d", ttl);
    return 0;
}

Output


Enter price and quantity: 150 10
Total: 1500

Integer Input

Use the %d format specifier for signed integers. Example:

Code Snippet: C


#include 

int main() {
    int num;
    printf("Enter an integer: ");
    scanf("%d", &num);
    printf("You entered: %d", num);
    return 0;
}

Output


Enter an integer: 234
You entered: 234

Multiple Integer Inputs

Code Snippet: C


#include 

int main() {
    int num1, num2;
    printf("Enter two integers: ");
    scanf("%d %d", &num1, &num2);
    printf("You entered: %d and %d", num1, num2);
    return 0;
}

Output


Enter two integers: 45 57
You entered: 45 and 57

Float Input

Use the %f format specifier for floating-point numbers. Example:

Code Snippet: C


#include 

int main() {
    float num;
    printf("Enter a number: ");
    scanf("%f", &num);
    printf("You entered: %f", num);
    return 0;
}

Output


Enter a number: 34.56
You entered: 34.560001

Integer and Float Inputs

Code Snippet: C


#include 

int main() {
    int num1;
    float num2;
    printf("Enter an integer and a float: ");
    scanf("%d %f", &num1, &num2);
    printf("You entered: %d and %.2f", num1, num2);
    return 0;
}

Output


Enter an integer and a float: 65 34.5678
You entered: 65 and 34.57

Character Input

Use the %c format specifier for single characters. Add a space before %c in the format string. Example:

Code Snippet: C


#include 

int main() {
    char ch;
    printf("Enter a character: ");
    scanf(" %c", &ch);
    printf("You entered: %c", ch);
    return 0;
}

Output


Enter a character: x
You entered: x

Multiple Character Inputs

Code Snippet: C


#include 

int main() {
    char ch1, ch2;
    printf("Enter two characters: ");
    scanf("%c %c", &ch1, &ch2);
    printf("You entered: %c and %c", ch1, ch2);
    return 0;
}

Output


Enter two characters: x y
You entered: x and y

String Input Using scanf()

Code Snippet: C


#include 

int main() {
    char name[20];
    printf("Enter your name: ");
    scanf("%s", name);
    printf("You entered: %s", name);
    return 0;
}

Output


Enter your name: Ravikant
You entered: Ravikant

String Input Using gets()

Code Snippet: C


#include 

int main() {
    char name[20];
    printf("Enter your name: ");
    gets(name);
    printf("You entered: %s", name);
    return 0;
}

Output


Enter your name: Ravikant Soni
You entered: Ravikant Soni

Reading a Character Sequence

Code Snippet: C


#include 

int main() {
    char ch;
    char word[10];
    int i = 0;
    printf("Enter characters. End by pressing the Enter key: ");
    
    while(1) {
        ch = getchar();
        word[i] = ch;
        if (ch == '\n')
            break;
        i++;
    }
    printf("\nYou entered: %s", word);
    return 0;
}

Output


Enter characters. End by pressing the Enter key: Hello

You entered: Hello

Character Input Using getchar()

Code Snippet: C


#include 

int main() {
    char ch;
    printf("Enter a character: ");
    ch = getchar();
    puts("You entered: ");
    putchar(ch);
    printf("\nYou entered: %c", ch);
    return 0;
}

Output


Enter a character: W
You entered:
W
You entered: W