It is axiomatic tbat a plaintiff in a civil action must both allege and prove every material fact essential to the establishment of a cause of action in his favor against the defendant in order to obtain the judgment which he seeks. In the case at bar, the defendant concedes that the plaintiff has stated enough facts in his complaint to constitute a good cause of action against it for damages for breach of an express warranty made by it to plaintiff. By its motion for a compulsory nonsuit under G.S. 1-183 and its prayers for a directed verdict on the first and second issues, however, the defendant challenges the sufficiency of the evidence to support the cause of action alleged. In determining whether or not the trial court erred in denying the defendant’s motion for an involuntary nonsuit or in refusing to direct a verdict for the defendant upon the first and second issues in conformity to its requests for instructions, we must take it for granted that the evidence tending to support the plaintiff’s claim is true and must resolve all conflicts of testimony in his favor. Bundy v. Powell, 229 N.C. 707, 51 S.E. 2d 307.

The Uniform Sales Act provides that “any affirmation of fact or any promise by the seller relating to the goods is an express warranty if the natural tendency of such affirmation or promise is to induce the buyer to purchase the goods, and if the buyer purchases the goods relying thereon.” Williston on Sales (Revised Edition), section 194. Our legislature has hot incorporated the Uniform Sales Act in our statutory law, but the accuracy.of the lucid and succinct definition of an express warranty embodied in the Act is fully supported by repeated decisions of this Court. Walston v. Whitley & Co., 226 N.C. 537, 39 S.E. 2d 375; Simpson v. Oil Co., 217 N.C. 542, 8 S.E. 2d 813; Dallas v. Wagner, 204 N.C. 517, 168 S.E. 833; Swift v. Meekins, 179 N.C. 173, 102 S.E. 138; Tomlinson v. Morgan, 166 N.C. 557, 82 S.E. 953; Hodges v. Smith, 159 N.C. 525; 75 S.E. 726; Wrenn v. Morgan, 148 N.C. 101, 61 S.E. 641; Reiger v. Worth, 130 N.C. 268, 41 S.E. 377, 89 Am. S.R. 865; Foggart v. Blackweller, 26 N.C. 238; Thompson v. Tale, 5 N.C. 97, 3 Am. D. 678.

The defendant bases its claim to a compulsory nonsuit or directed verdict initially upon the theory that the evidence compels the single deduction that its contract of sale was with Barbour Boat Works and not with the plaintiff. This position is unsupportable. It ignores the testimony relating to the conversation between plaintiff and the defendant’s sales agent, Hoffman. It likewise refuses to take notice of the offer of the defendant to sell the engine to “Clyde R. Potter (Buyer)” for a price to be paid partly in cash and partly in future installments, and the statements in the letter and purchase order sent to defendant by Barbour Boat *8 Works that the purchase was to be for cash because “Mr. Potter (had) decided that he would not purchase this unit on- a deferred payment basis.” Moreover, it leaves out of consideration the purchase order of 2 February, 1946, and the invoice of 6 February, 1946, which justify the inference that the Barbour Boat Works, in effect, received a commission of $1,750.00 for aiding defendant to consummate the sale of the engine to plaintiff. The defendant asserts secondarily that the trial court erred in refusing to nonsuit the action or to direct a verdict for it therein upon the ground that there is no evidence in the record to sustain the proposition that the defendant ever affirmed or promised that the engine would have a speed of 600 rermlutions per minute or would develop 260 horsepower when used in conjunction with a propeller of a diameter of 50 inches and a pitch of 34 inches. This position is untenable. It conflicts directly with the evidence of the conversation between plaintiff and Hoffman. Furthermore, it runs counter to the fact that all transactions looked to the installation of an engine in “Hull No. 15,” whose plans and specifications called for a 3-bladed bronze propeller “of about 50 inch diameter and a pitch of about 34 inches.”

When the evidence tending to support the plaintiff’s claim is accepted as true and the-conflicts of testimony'are resolved in his favor, it becomes manifest that the trial court properly refused to nonsuit the action or to direct a verdict for defendant therein. This is true because the testimony adduced at the trial was sufficient to justify the inferences that defendant sold the engine to plaintiff and that as a part of the sale the defendant expressly warranted that the engine “would turn a 50 x 34 propeller 600 r.p.m. and at such speed would develop 260 h.’ p.” when installed in- the trawler designated as “Hull No. 15.”

While the question is not mooted on the appeal, it is not altogether amiss to note, in passing, that a buyer does not waive his right to sue his seller for damages for a breach of warranty by the mere acceptance and retention of goods not fulfilling the warranty. Manufacturing Co. v. Gray, 124 N.C. 322, 32 S.E. 718; Alpha Mills v. Engine Co., 116 N.C. 797, 21 S.E. 917; Love v. Miller, 104 N.C. 582, 10 S.E. 685; Lewis v. Rountree, 78 N.C. 323.

The defendant reserved exceptions to the admission of certain testimony offered by plaintiff on the theory that its reception contravened the parol evidence rule. In this connection, the defendant asserts that the conversation between plaintiff and the defendant’s sales agent, Hoffman, antedated the written contract of 2 February, 1946, between plaintiff and Barbour Boat Works; that such written contract specified that the trawler to be completed thereunder was to be driven by a “Superior Marine Diesel Engine, Standard Model, 6 cylinder, nine inch base x 12 inch stroke, rated 200 H. P. at 450 R.P.M.”; that such written provision was controlling *9 as to the character of the engine to be installed in the trawler; that the alleged prior oral agreement between plaintiff and Hoffman, and the other testimony concerning an engine which “would turn a 50 x 34 propeller 600 R.P.M. and at such speed . . . develop 260 H. P.” was at variance with the written contract between plaintiff and Barbour Boat "Works; and that by reason thereof the testimony in question was inadmissible under the parol evidence rule.

It is a well established principle, which is known as the parol evidence rule, that when any contract has been reduced to writing, and is evidenced by a document or series of documents, parol evidence cannot he admitted to alter, add to, or contradict the writing in actions between parties to the contract or persons claiming under them where claims or rights .created by the contract are the subject matter of the litigation. Jones v. Chevrolet Co., 217 N.C. 693, 9 S.E. 2d 395; Holloman v. R. R., 172 N.C. 372, 90 S.E. 292, L.R.A. 1917C 416, Ann, Cas. 1917E 1069; King v. McRackan, 168 N.C. 621, 84 S.E. 1027; Ledford v. Emerson, 138 N.C. 502, 51 S.E. 42; Carden v. McConnell, 116 N. C. 875, 21 S.E. 923; Reynolds v. Magness, 24 N. C. 26. Under this rule, parol testimony as to conversations or declarations of the parties at or before the execution of a written contract will not be received for the purpose of substituting a different agreement for the one expressed in the writing. Whitehurst v. FCX Fruit and Vegetable Service, 224 N.C. 628, 32 S.E. 2d 34; Insurance Co. v. Morehead, 209 N.C. 174, 183 S.E. 606; Bank v. Sternberger, 207 N.C. 811, 178 S.E. 595, 97 A.L.R. 720; Oliver v. Hecht, 207 N.C. 481, 177 S.E. 399; Winstead v. Manufacturing Co., 207 N.C. 110, 176 S.E. 304.

The record on this appeal makes it plain, however, that the trial court did not err in admitting the testimony now under consideration. The defendant is precluded from invoking the parol evidence rule on the basis of the contract of 2 February, 1946, between plaintiff and the Barbour Boat "Works. It is not a party to that contract, and that contract does not undertake to govern any contractual relations between it and the plaintiff. Besides, the plaintiff does not seek to enforce against the defendant any claim or right created by his contract of 2 February, 1946, with Barbour Boat "Works. Indeed, he bases his cause of action upon a different contract made between him and the defendant and resting partly in parol and partly in writing. Furthermore, it might well be noted that the agreement between plaintiff and defendant covering an engine “to develop 260 H. P. at 600 R.P.M.” became legally effective subsequent to the contract of 2 February, 1946.

"We have given painstaking study to the remaining exceptions addressed to the admission of testimony and to the assignments of error based on excerpts from the charge and have found no error prejudicial to any substantial right of the defendant.

*10 For the reasons.given, the trial and judgment in the Superior Court will be upheld.

No error.