var gbp, usd, eur, cad, aud; function init() { gbp = document.getElementById("GBP"); usd = document.getElementById("USD"); eur = document.getElementById("EUR"); cad = document.getElementById("CAD"); aud = document.getElementById("AUD"); } function gbpfunc() { usd.value = parseFloat(gbp.value) * 0.49246; eur.value = parseFloat(gbp.value) * 0.69714; cad.value = parseFloat(gbp.value) * 0.50221; aud.value = parseFloat(gbp.value) * 0.43497; } function eurfunc() { gbp.value = parseFloat(eur.value) * 1.43448; usd.value = parseFloat(eur.value) * 0.70641; cad.value = parseFloat(eur.value) * 0.72037; aud.value = parseFloat(eur.value) * 0.62382; } function cadfunc() { gbp.value = parseFloat(cad.value) * 1.99169; usd.value = parseFloat(cad.value) * 0.98054; eur.value = parseFloat(cad.value) * 1.38814; aud.value = parseFloat(cad.value) * 0.86613; } function audfunc() { gbp.value = parseFloat(aud.value) * 2.29964; usd.value = parseFloat(aud.value) * 1.13262; eur.value = parseFloat(aud.value) * 1.60329; cad.value = parseFloat(aud.value) * 0.88297; } function usdfunc() { gbp.value = parseFloat(usd.value) * 2.03032; eur.value = parseFloat(usd.value) * 1.41544; cad.value = parseFloat(usd.value) * 1.01941; aud.value = parseFloat(usd.value) * 0.88297; } init();

<input type="text" id="GBP" size="10" value="0" onchange="gbpfunc()"/> <label for="GBP"> GBP </label> </br> <input type="text" id="USD" size="10" value="0" onchange="usdfunc()" /> <label for="USD"> USD </label> </br> <input type="text" id="EUR" size="10" value="0" onchange="eurfunc()" /> <label for="EUR"> EUR </label> </br> <input type="text" id="CAD" size="10" value="0" onchange="cadfunc()" /> <label for="CAD"> CAD </label> </br> <input type="text" id="AUD" size="10" value="0" onchange="audfunc()" /> <label for="AUD"> AUD </label>

Hocam bakın javascript halide bu şekilde sadece kendinize göre ayarlayın. Mantığı oluşsun kafanızda



https://www.w3schools.com/howto/howt..._converter.asp

Buraya da bakabilirsiniz, stackoverflow üzerinden de araştırabilirsiniz.