scanf doesn't recognize numbers correctly

November 10, 2024

I was trying to make a program that makes a triangle comprised of numbers that are imputted. For example, if I input a string 123 the output should be the following.

1
12
123

I tried to implement it with the following code:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>

int main()
{
    char s[501];
    scanf("%[^\n]", s);
    for (int i=0;s[i]!='\0';i++) {
        for (int j=1;j<=s[i];j++) {
            printf("%d", j);
        }
        printf("\n");
    }
    return 0;
}

However, the output was the following (the input was 123):

12345...4849
12345...484950
12345...48495051

Any ideas? Thanks

>Solution :

The problem doesn’t lie in scanf(). In this loop:

for (int i=0;s[i]!='\0';i++) {

s[i] gets converted to decimal value of the ASCII character (there
are other systems too like EBCDIC but most likely you’re not using
it). You can see it in man ascii – 1 is 49, 2 is 50 and 3 is 51. You
need to convert this number to a number that’s the same as the string
value of the character:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>

int main()
{
    char s[501];
    scanf("%[^\n]", s);
    for (int i=0;s[i]!='\0';i++) {
        for (int j=1;j<=s[i]-'0';j++) {
            printf("%d", j);
        }
        printf("\n");
    }
    return 0;
}

Output: