Changing sentence inside a printf

March 5, 2022

i’m new to C and i have these line of codes

int Input(char c) 
{
    printf("input number %c: ",c);
    scanf("%d", &a);
    return a;
}

void main()
{
    int n;
    n = Input('A'); // n = a ;
    printf("The number you just input is %d", n); 
    return;
}

Output:

Input number A: 5

The number you just input is 5

But i’m wondering if i can replace the "input number %c: " which another string like "input a number above 0" using the called function in main()

int Input(char c) 
{
    printf("%s: ",c);
    scanf("%d", &a);
    return a;
}

void main()
{
    int n;
    n = Input("input a number above 0: ");
    printf("The number you just input is %d", n); 
    return;
}

Expected Output:

input a number above 0: *input a number*

>Solution :

Firstly, a is undefined in your Input function.

As for passing a string instead of a single character:

%c expects a char.

%s expects a char * – a pointer to a null-terminated string.

Remember to check that the return value of scanf matches the number of conversions you were expecting, and handle the event otherwise (e.g., exit).

int Input(const char *msg) {
    int val;
    
    printf("input number %s", msg);
    
    if (1 != scanf("%d", &val)) {
        fprintf(stderr, "Could not read integer value.\n");
        exit(EXIT_FAILURE);
    }
    
    return val;        
}

Usage:

int n = Input("a string");

If you want to retain string interpolation, use a variadic function.

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

int get_int(const char *msg, ...) {
    va_list args;
    va_start(args, msg);
    vprintf(msg, args);
    va_end(args);

    int val;

    if (1 != scanf("%d", &val)) {
        fprintf(stderr, "Could not read integer value.\n");
        exit(EXIT_FAILURE);
    }

    return val;
}

int main(void) {
    int n = get_int("Enter an integer (%c): ", 'A');

    printf("Got: %d\n", n);
}