String Format for Double [C#]

The following examples show how to format float numbers to string in C#. You can use static method String.Format or instance methods double.ToString and float.ToString.

Digits after decimal point

This example formats double to string with fixed number of decimal places. For two decimal places use pattern „0.00“. If a float number has less decimal places, the rest digits on the right will be zeroes. If it has more decimal places, the number will be rounded.
[C#]

// just two decimal places
String.Format("{0:0.00}", 123.4567);      // "123.46"
String.Format("{0:0.00}", 123.4);         // "123.40"
String.Format("{0:0.00}", 123.0);         // "123.00"

// just two decimal places
String.Format("{0:0.00}", 123.4567); // "123.46"
String.Format("{0:0.00}", 123.4); // "123.40"
String.Format("{0:0.00}", 123.0); // "123.00"

<span class="comments">// just two decimal places</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.00}"</span>, 123.4567);      <span class="comments">// "123.46"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.00}"</span>, 123.4);         <span class="comments">// "123.40"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.00}"</span>, 123.0);         <span class="comments">// "123.00"</span>

Next example formats double to string with floating number of decimal places. E.g. for maximal two decimal places use pattern „0.##“.
[C#]

// max. two decimal places
String.Format("{0:0.##}", 123.4567);      // "123.46"
String.Format("{0:0.##}", 123.4);         // "123.4"
String.Format("{0:0.##}", 123.0);         // "123"

// max. two decimal places
String.Format("{0:0.##}", 123.4567); // "123.46"
String.Format("{0:0.##}", 123.4); // "123.4"
String.Format("{0:0.##}", 123.0); // "123"

<span class="comments">// max. two decimal places</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.##}"</span>, 123.4567);      <span class="comments">// "123.46"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.##}"</span>, 123.4);         <span class="comments">// "123.4"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.##}"</span>, 123.0);         <span class="comments">// "123"</span>

Digits before decimal point

If you want a float number to have any minimal number of digits before decimal point use N-times zero before decimal point. E.g. pattern „00.0“ formats a float number to string with at least two digits before decimal point and one digit after that.
[C#]

// at least two digits before decimal point
String.Format("{0:00.0}", 123.4567);      // "123.5"
String.Format("{0:00.0}", 23.4567);       // "23.5"
String.Format("{0:00.0}", 3.4567);        // "03.5"
String.Format("{0:00.0}", -3.4567);       // "-03.5"

// at least two digits before decimal point
String.Format("{0:00.0}", 123.4567); // "123.5"
String.Format("{0:00.0}", 23.4567); // "23.5"
String.Format("{0:00.0}", 3.4567); // "03.5"
String.Format("{0:00.0}", -3.4567); // "-03.5"

<span class="comments">// at least two digits before decimal point</span>
<span class="type">String</span>.Format(<span class="string">"{0:00.0}"</span>, 123.4567);      <span class="comments">// "123.5"</span>
<span class="type">String</span>.Format(<span class="string">"{0:00.0}"</span>, 23.4567);       <span class="comments">// "23.5"</span>
<span class="type">String</span>.Format(<span class="string">"{0:00.0}"</span>, 3.4567);        <span class="comments">// "03.5"</span>
<span class="type">String</span>.Format(<span class="string">"{0:00.0}"</span>, -3.4567);       <span class="comments">// "-03.5"</span>

Thousands separator

To format double to string with use of thousands separator use zero and comma separator before an usual float formatting pattern, e.g. pattern „0,0.0“ formats the number to use thousands separators and to have one decimal place.
[C#]

String.Format("{0:0,0.0}", 12345.67);     // "12,345.7"
String.Format("{0:0,0}", 12345.67);       // "12,346"

String.Format("{0:0,0.0}", 12345.67); // "12,345.7"
String.Format("{0:0,0}", 12345.67); // "12,346"

<span class="type">String</span>.Format(<span class="string">"{0:0,0.0}"</span>, 12345.67);     <span class="comments">// "12,345.7"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0,0}"</span>, 12345.67);       <span class="comments">// "12,346"</span>

Zero

Float numbers between zero and one can be formatted in two ways, with or without leading zero before decimal point. To format number without a leading zero use # before point. For example „#.0“ formats number to have one decimal place and zero to N digits before decimal point (e.g. „.5“ or „123.5“).
Following code shows how can be formatted a zero (of double type).
[C#]

String.Format("{0:0.0}", 0.0);            // "0.0"
String.Format("{0:0.#}", 0.0);            // "0"
String.Format("{0:#.0}", 0.0);            // ".0"
String.Format("{0:#.#}", 0.0);            // ""

String.Format("{0:0.0}", 0.0); // "0.0"
String.Format("{0:0.#}", 0.0); // "0"
String.Format("{0:#.0}", 0.0); // ".0"
String.Format("{0:#.#}", 0.0); // ""

<span class="type">String</span>.Format(<span class="string">"{0:0.0}"</span>, 0.0);            <span class="comments">// "0.0"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.#}"</span>, 0.0);            <span class="comments">// "0"</span>
<span class="type">String</span>.Format(<span class="string">"{0:#.0}"</span>, 0.0);            <span class="comments">// ".0"</span>
<span class="type">String</span>.Format(<span class="string">"{0:#.#}"</span>, 0.0);            <span class="comments">// ""</span>

Align numbers with spaces

To align float number to the right use comma „,“ option before the colon. Type comma followed by a number of spaces, e.g. „0,10:0.0“ (this can be used only in String.Format method, not in double.ToString method). To align numbers to the left use negative number of spaces.
[C#]

String.Format("{0,10:0.0}", 123.4567);    // "     123.5"
String.Format("{0,-10:0.0}", 123.4567);   // "123.5     "
String.Format("{0,10:0.0}", -123.4567);   // "    -123.5"
String.Format("{0,-10:0.0}", -123.4567);  // "-123.5    "

String.Format("{0,10:0.0}", 123.4567); // " 123.5"
String.Format("{0,-10:0.0}", 123.4567); // "123.5 "
String.Format("{0,10:0.0}", -123.4567); // " -123.5"
String.Format("{0,-10:0.0}", -123.4567); // "-123.5 "

<span class="type">String</span>.Format(<span class="string">"{0,10:0.0}"</span>, 123.4567);    <span class="comments">// "     123.5"</span>
<span class="type">String</span>.Format(<span class="string">"{0,-10:0.0}"</span>, 123.4567);   <span class="comments">// "123.5     "</span>
<span class="type">String</span>.Format(<span class="string">"{0,10:0.0}"</span>, -123.4567);   <span class="comments">// "    -123.5"</span>
<span class="type">String</span>.Format(<span class="string">"{0,-10:0.0}"</span>, -123.4567);  <span class="comments">// "-123.5    "</span>

Custom formatting for negative numbers and zero

If you need to use custom format for negative float numbers or zero, use semicolon separator „;“ to split pattern to three sections. The first section formats positive numbers, the second section formats negative numbers and the third section formats zero. If you omit the last section, zero will be formatted using the first section.
[C#]

String.Format("{0:0.00;minus 0.00;zero}", 123.4567);   // "123.46"
String.Format("{0:0.00;minus 0.00;zero}", -123.4567);  // "minus 123.46"
String.Format("{0:0.00;minus 0.00;zero}", 0.0);        // "zero"

String.Format("{0:0.00;minus 0.00;zero}", 123.4567); // "123.46"
String.Format("{0:0.00;minus 0.00;zero}", -123.4567); // "minus 123.46"
String.Format("{0:0.00;minus 0.00;zero}", 0.0); // "zero"

<span class="type">String</span>.Format(<span class="string">"{0:0.00;minus 0.00;zero}"</span>, 123.4567);   <span class="comments">// "123.46"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.00;minus 0.00;zero}"</span>, -123.4567);  <span class="comments">// "minus 123.46"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0.00;minus 0.00;zero}"</span>, 0.0);        <span class="comments">// "zero"</span>

Some funny examples

As you could notice in the previous example, you can put any text into formatting pattern, e.g. before an usual pattern „my text 0.0“. You can even put any text between the zeroes, e.g. „0aaa.bbb0“.
[C#]

String.Format("{0:my number is 0.0}", 12.3);   // "my number is 12.3"
String.Format("{0:0aaa.bbb0}", 12.3);          // "12aaa.bbb3"

String.Format("{0:my number is 0.0}", 12.3); // "my number is 12.3"
String.Format("{0:0aaa.bbb0}", 12.3); // "12aaa.bbb3"

<span class="type">String</span>.Format(<span class="string">"{0:my number is 0.0}"</span>, 12.3);   <span class="comments">// "my number is 12.3"</span>
<span class="type">String</span>.Format(<span class="string">"{0:0aaa.bbb0}"</span>, 12.3);          <span class="comments">// "12aaa.bbb3"</span>

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Mahmoud Salem Mahmoud