How to insert character in-between value using printf?

Question

I have a problem. I need to insert a specific char (number sign) into my output value. I am not allowed to use if statement and "? :" statement. My output needs to look like this:

9999.999(+/-)i9999.999

Where character "i" needs to go right after the 2nd number sign. Here is my code so far:

void show(struct z z) {
    printf("%.3fi%.3f", z.re, z.im);
}

i love the 'i am not allowed to use the if statement'. Another assignment with 'clever' rules — pm100, Oct 09 '18 at 21:12
2nd value can be either +/-, the thing is that I need to put "i" right after the sign. — RPAnimation, Oct 09 '18 at 21:13
to clarify Eugene comment. What you have should work (apart from +). So what is your problem? Does it not compile? run? give the wrong result? — pm100, Oct 09 '18 at 21:13
perhaps this question and the answers would help: https://stackoverflow.com/q/4099433/1212725 — bruceg, Oct 09 '18 at 21:15
so your actual question is "how can I put a + or - depending on the value of z.im?" — pm100, Oct 09 '18 at 21:15
Isn't it more usual to place the *`i`* on the right with an imaginary number, like `9999.999 + 9999.999i`? — Weather Vane, Oct 09 '18 at 21:15
@WeatherVane yes but then this would be too easy, just add 'i' after the number. Here we need the sign character then 'i' then the abs value of z.im — pm100, Oct 09 '18 at 21:16
I think you're saying that the `+` or `-` corresponds to the sign of `z.im`, but you didn't actually say so. Can you update your question to clarify that point? — Keith Thompson, Oct 09 '18 at 21:19
You mention in a comment that you're not allowed to use the `?:` operator. Please update your question to say that as well. — Keith Thompson, Oct 09 '18 at 21:21
@pm100 still need to force a sign for the imaginary part, like format `"%+f"`. — Weather Vane, Oct 09 '18 at 21:26
can't you just do this? `printf("%f%+fi\n", z.re, z.im);`, and let the format specifier choose the correct sign for you? — bruceg, Oct 09 '18 at 21:26

score 2 · Accepted Answer · answered Oct 09 '18 at 21:21

2

without if or ternary

void show(struct z z) {
    printf("%.3f%ci%.3f", z.re, "+-"[z.im<0], fabs(z.im));
}

answered Oct 09 '18 at 21:21

pm100

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Nice solution, but I somehow doubt the instructor have meant this. – Eugene Sh. Oct 09 '18 at 21:29
@EugeneSh. Well if is banned, ternary is banned, this is a 'clever ' trick so maybe it is OK. Who knows – pm100 Oct 09 '18 at 21:34

Barmar · Answer 2 · 2018-10-09T21:27:01.497

1

Use a conditional (aka "ternary") expression to print + or - depending on the sign of the imaginary part. Then print the absolute value of the imaginary part.

void show(struct z z) {
    printf("%.3f%ci%.3f", z.re, (z.im >= 0 ? '+' : '-'), fabs(z.im));
}

If you can't use a ternary, either, you can format the number with a forced sign into a string, then swap the i and sign in the result.

void show(struct z z) {
    char result[100];
    sprintf(result, "%.3fi%+.3f", z.re, z.im);
    int iloc = strchr(result, 'i');
    result[iloc] = result[iloc+1];
    result[iloc+1] = 'i';
    printf("%s", result);
}

edited Oct 09 '18 at 21:27

answered Oct 09 '18 at 21:16

Barmar

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yup, the 'if' rule was clearly intended to force use of ternary. Now I wonder if its doable without ternary or if - intersting challenge – pm100 Oct 09 '18 at 21:18
The thing is, that's not allowed either... I just didn't know how it was called. – RPAnimation Oct 09 '18 at 21:19
ternary not allowed either? – pm100 Oct 09 '18 at 21:20
1

@pm100 No problem: printf("...", z.re, '-'-(z.im >= 0)*2, fabs(z.im)); – Ctx Oct 09 '18 at 21:21
@RPAnimation Is this exercise associated with a lesson on a particular topic? What is the topic? – Barmar Oct 09 '18 at 21:22
@Ctx I would bet the instructor would forbid it as well if could think about it :) – Eugene Sh. Oct 09 '18 at 21:22
if you use the `%+f` format specifier, it will choose the correct sign for you – bruceg Oct 09 '18 at 21:24
1

@bruceg Yes, but it puts it after the `i`, not before. – Barmar Oct 09 '18 at 21:27
1

I would be willing to bet that the OP is confused about where the `i` is supposed to go. – bruceg Oct 09 '18 at 21:29
1

@bruceg Possibly. Complex numbers are normally `(+-)i` – Barmar Oct 09 '18 at 21:32

chux - Reinstate Monica · Answer 3 · 2018-10-09T22:55:32.170

To properly handle -0.0 and NAN, extract the sign with signbit() and use the string trick as in @pm100.

The signbit macro determines whether the sign of its argument value is negative. (footnote)
The signbit macro returns a nonzero value if and only if the sign of its argument value is negative.
The signbit macro reports the sign of all values, including infinities, zeros, and NaNs.

#include <math.h>

// 9999.999(+/-)i9999.999
printf("%.3f%ci%.3f", z.re, "-+"[!signbit(z.im)], fabs(z.im));

How to insert character in-between value using printf?

3 Answers3